IRLF 


E7E 


HHBB^B 

• 


REESE   LIBRARY 

oi     i  HI: 

UNIVERSITY  OF  CALIFORNIA. 


No.(P*Lsi)  /O  .     C/JSS  No. 


ELECTRIC  RAILWAY  MOTORS 


THEIR 


Construction,  Operation  and 
Maintenance 


AN    ELEMENTARY    PRACTICAL    HANDBOOK    FOR    THOSE   EN- 
GAGED IN   THE   MANAGEMENT  AND  OPERATION 
OP  ELECTRIC  RAILWAY  APPARATUS 


WITH 

RULES  AND  INSTRUCTIONS  FOR  MOTORMEN 

BY 

NELSON  W.  PERRY,  E.  M. 


OFTHE 

UNIVERSITY 
CALIFORNIA 


.        NEW  YORK 

THE  W.  J.  JOHNSTON  COMPANY 
253  BROADWAY 

1896' 


COPYRIGHT,  1894, 

BY 
STREET  RAILWAY  GAZETTE  COMPANY. 


r/ 


UNIVERSITY 

CALIFORNIA. 


CONTENTS. 


CHAPTER  PAGE 

Preface, .  v 

I.     Introduction,        ......  1 

II.     Technical  Terms,  etc., 9 

III.  Ohm's  Law  ;  Rate  of  Work  ;  Examples,     .  16 

IV.  The  Electric  Current  and  its  Properties,         .  28 
V.     The  Electric  Current  and  its  Properties  (con-  * 

tinned) ;  the~£«&en<jid, »  .        .        /        .  39 
VI.    Measuring  the  Current ;  Magnetism  and  Elec- 
tro-Magnetism,     48 

VII.    Lines  of  Force  ;  the  Closed  Magnetic  Circuit ; 

Magnetic  Leakage,          ;        ....          59 
VIII.     Polarity,  Magnetism  and  Current,  .        *        .      67 
IX.     Electro-Magnetic  Induction  ;  The  Continuous 
Current  Dynamo  ;  Increase  of  Electromo- 
tive Force  ;  Eddy  Currents  in  Armature,        75 
X.     Shifting  of  the  Armature  Wires  ;  Open  and 

Closed  Coil  Armatures,   ;..-".        .      96 
XI.     Drum  and  Ring  Armatures  ;  Consequent  Poles 

and  Multipolar  Field  Magnets,       .  102 

XII.  Multiple  Arc  and  Series  Arrangement ;  Cur- 
rent Characteristics  of  Multiple  and  Series 
Arrangements  in  Generators,  .  .  . .  109 

XIII.  Current   Characteristics  in  Translating   De- 

vices ;  Multipolar  Fields,    '.k.  V'- .        .         116 

XIV.  The     Dynamo    Electric    Principle;    Series, 

Shunt  and  Compound  Winding  ;  the  Re- 
tersibility  of  the  Dynamo.          .  * .     129 

iii 


IV 


CONTENTS. 


CHAPTER  PAGE 

XV.    The  Electric  Motor, 139 

XVI.     The  Electric  Motor  (continued]  ;  Torque,         145 
XVII.    The  Line  of  Commutation  ;  Counter-Elec- 
tromotive Force,      .....     151 
XVIII.     Counter-Electromotive    Force    and    Speed 
Regulation ;  Requirements  of  Speed  Reg- 
ulation,          157 

XIX.    The  Sperry  and  Johnson-Lundell  Systems,    169 
XX.    The  Leonard,  Perry  and  Other  Systems  ; 
the  Perry  System  of  Series  Electric  Trac- 
tion ;  Storage  Battery  Traction  ;  Conduit 

Systems, 177 

XXI.    The  Management  of  Street  Railway  Motors ; 
Sparking   at   the  Commutator ;    Motor 
Stops  Ox  Fails  to  Start,    .        .        .        .     191 
XXII.    Specific  Directions  to  Motormen,     .        .         201 

XXIII.  Instructions  to  Inspectors  and  Superintend- 

ents,  213 

XXIV.  Locating     Faults ;     Commutators ;     Drop 

Method  of  Testing  for  Faults ;  Insulation 
Test ;    Bearings  ;    Gears    and    Pinions ; 

Controllers, 220 

XXV.     Trolley  Wheels;  In  can  descent  Lamps;  Con- 

elusion,    .        .    -    /"  :,  .        .        .  229 


OF  THE 

UNIVERSITY, 
CALIFORNIA 


PEEFACE. 


THE  m&ttei'  contained  in  this  book  first  ap- 
peared as  a  serial  in  the  /Street  Railway  Gazette, 
beginning  with  the  first  issue  in  January  and  ex- 
tending through  succeeding  issues  until  that  of 
July  21.  The  ostensible  object  of  the  series  was 
to  provide  for  motormen  an  intelligent  elementary 
exposition  of  the  principles  upon  which  are  founded 
the  apparatus  which  they,  too  often  without  any 
conception  of  their  character,  are  called  upon  to 
handle.  It  has  been  assumed  by  the  author  that 
the  audience  is  entirely  ignorant  both  of  the 
nomenclature  and  principles  of  applied  electricity, 
but  is  anxious  to  gain  a  foothold,  as  it  were,  on 
the  science.  To  this  end  he  has  avoided  the  use 
of  all  technical  terms,  except  such  as  necessarily 
form  the  very  alphabet  of  the  science,  and  these 
have  been  met  boldly — the  principle  being  fol- 
lowed, however,  of  first  explaining  by  simple  ex- 
periments, such  as  are  readily  within  the  scope  of 
a  child  of  fifteen  years,  the  phenomena  themselves, 
and  then  assigning  to  these  phenomena  their  proper 
names. 

In  the  study  of  a  new  language,  a  new  science 
or  a  new  branch  of  mathematics  it  is  the  first 
principles  that  are  almost  always  the  most  difficult 
to  acquire.  Few  of  us,  probably,  recall  the  task  it 


VI  PREFACE. 

was  for  us  to  learn  the  alphabet  of  our  language. 
More  of  us  will  remember  the  difficulty  experi- 
enced in  acquiring  the  multiplication  table,  and  all 
who  have  pursued  the  higher  mathematics  will 
remember  how,  after  passing  through  algebra, 
geometry,  and  trigonometry,  they  were  perplexed 
by  the  very  rudiments  of  the  differential  calculus. 
As  each  step  was  taken  the  mind  had  to  be  pre- 
pared for  the  new  study  by  means  of  analogies 
which,  though  never  exactly  true,  enabled  the 
mind  to  grasp  ideas  approximately  correct  only, 
but  which  served  as  stepping-stones  to  other 
ideas  which  approached  more  nearly  the  truth. 
In  this  work  free  use  has  been  made  of  analogy, 
but  by  extending  the  analogies  over  a  somewhat 
extended  range,  and  by  making  use  of  some  which 
are  believed  to  be  new,  it  is  thought  that  the 
ideas  inculcated  by  them  will  be  as  free  from 
error  as  is  possible  under  such  circumstances. 

The  author  has  insisted  upon  a  full  understand- 
ing of  Ohm's  law — the  fundamental  law  of  the 
flow  of  currents — as  a  prerequisite  to  a  further 
understanding  of  the  subject.  This  law,  however, 
is  not  sprung  at  once  upon  the  student,  but  is  led 
up  to  by  the  series  of  simple  and  inexpensive  ex- 
periments before  referred  to,  in  the  performance 
of  which  the  student  at  last  finds  himself  sur- 
prised that  he  has  not  only  practically  worked  out 
for  himself  the  law,  but  has  actually  constructed 
an  elementary  dynamo  and  motor  for  himself, 
together  with  instruments  for  measuring  electrical 
currents.  The  law  is  then  enunciated  and  further 
illustrated  by  a  number  of  concrete  examples,  in- 
volving only  the  simplest  mathematics,  but  at  the 
same  time  'practically  covering  every  problem  in 
electrical  distribution  by  direct  currents  that  the 


tBEFACB.  Vll 

electrician  is  ever  likely  to  be  called  upon  to  solve. 
The  extreme  simplicity  of  these  operations — all 
depending  upon  Ohm's  law — will  doubtless  be  a 
revelation  to  most  of  those  for  whom  this  book  is 
intended. 

The  dynamo  and  motor  are  treated  as  one  and 
the  same  machine,  as  they  really  are,  and  it  is 
shown  that  they  all,  of  whatever  type,  are  built 
upon  exactly  the  same  principles,  and  these  are 
explained  and  developed  from  the  simplest  forms 
by  the  aid  of  numerous  cuts  and  diagrams  leading 
up  to  the  finished  multipolar  machine  of  to-day. 
The  intricacies  and  refinements  of  the  completed 
machines,  are,  however,  avoided  as  tending  in 
a  book  of  the  scope  of  this  one  to  undesirable 
confusion. 

The  theory  and  methods  of  speed  control  of 
railway  motors  are  treated  in  as  comprehensive 
manner  as  seemed  desirable,  the  aim  being  always 
to  explain  the  why  and  wherefore  of  a  given 
arrangement,  rather  than  to  describe  in  full  a 
specific  device.  Following  this  comes  a  brief 
description  of  some  of  the  newer  electric  railway 
systems  which  promise  to  come  into  more  or  less 
general  use,  but  which  are  not  now  generally 
known  to  the  lay  public. 

Thus  far  it  is  believed  that  the  book  will  be  of 
service  to  others  than  motormen — that  it  will  be 
of  interest  to  that  large  class  of  intelligent  Ameri- 
cans who  desire  to  acquire  a  somewhat  definite 
knowledge  of  this  mysterious  agent  that  they  see 
working  around  them  daily,  who  wish  to  know 
something  more  definite  of  electricity,  either  with 
the  view  of  taking  up  its  study  more  systematically 
in  the  future,  or  for  the  purpose  solely  of  getting 
a  more  intelligent  idea  of  its  workings.^ 


Vlll  PREFACE. 

The  last  part  of  the  work  is  devoted  to  direc- 
tions for  the  care  of  street  railway  motors,  the 
detection  and  remedy  and  prevention  of  their 
faults.  These  suggestions  come  from  a  most  ex- 
tended and  varied  practice,  not  of  the  author's 
alone,  but  of  other  engineers  and  of  the  manu- 
facturers of  the  motors  themselves.  This  portion 
of  the  book  is  especially  intended  for  those  whose 
business  it  is  to  handle  the  motors.  The  -author 
hopes  that  this  portion  of  the  book  will  be  found 
particularly  useful  to  those  for  whom  it  is  in- 
tended by  reason  of  the  fact  that  he  has  en- 
deavored in  the  earlier  chapters  to  so  lead  up  to 
the  subject  that  the  reason  for  the  various  rules 
and  precautions  laid  down  will  be  at  once  apparent 
to  the  motorman,  and  that  they  will  thus  appeal 
to  his  intelligence  much  more  strongly  than  they 
would  if  given  empirically. 

In  conclusion  the  author  wishes  to  acknowledge 
the  assistance  he  has  received  by  free  reference  to 
Crocker  and  Wheeler's  "  Practical  Management  of 
Dynamos  and  Motors,"  Crosby  and  Bell's  "The 
Electric  Railway,"  Silvanus  Thompson's  "Dynamo- 
Electric  Machinery,"  and  "  The  Electromagnet," 
and  especially  to  the  kind  response  to  inquiries  of 
The  Westinghouse  Electric  and  Manufacturing 
Co.,  The  General  Electric  Co.,  The  Short  Electric 
Railway  Co.,  The  Sperry  Electric  Railway  Co. 


ELECTRIC  RAILWAY  MOTORS, 


THEIR 


CONSTRUCTION,     OPERATION  AND 
MAINTENANCE. 


CHAPTER  I. 

INTRODUCTI ON. 

SOME  years  ago  I  became  acquainted,  as  a 
boarder,  with  a  bright  young  man  who  introduced 
himself  to  me  as  an  electrician.  It  happened  that 
we  were  placed  at  the  same  table,  and  as  he  was 
of  an  affable  disposition  we  soon  became  veiy  well 
acquainted.  Whenever  the  subject  of  electricity 
came  up,  he  was  accustomed  to  speak  in  such  a 
way  as  to  impress  all  his  hearers  with  the  idea 
that  he  was  an  authority  on  all  such  subjects 
whose  opinions  were  not  to  be  questioned,  and  as 
he  was  generally  correct  in  his  statements  I  also 
became  somewhat  impressed  with  his  knowledge, 
and  would  often  ask  questions — sometimes  for  in- 
formation, and  sometimes  to  see  how  nearly  his 
opinions  coincided  with  my  own. 

I  found  that  he  had  been  sent  out  by  the  then 


2  ELECTRIC    RAILWAY    MOTORS. 

leading  company  engaged  in  electrical  railway 
construction,  and  his  business  in  that  city — a 
Western  one — was  the  construction  of  its  first  elec- 
tric railway.  We  soon  became  quite  good  friends, 
and  when  the  power  house  was  nearing  completion 
I  was  a  privileged  character  within  its  walls,  for 
visitors  were  rigidly  excluded  as  a  rule  ;  and  later, 
when  the  first  tests  of  the  operation  of  the  road 
were  made,  I  was  one  of  the  fortunate  few  invited 
guests. 

The  first  car  over  the  line  started  out  from  the 
barns  at  ten  o'clock  at  night,  and  carried  as  pas- 
sengers, besides  myself  and  the  gentleman  referred 
to,  but  three  others — all  officials  of  the  road. 
Everything  went  smoothly  until  the  further  ter- 
minus— about  three  miles  distant — was  reached, 
when  something  gave  way  and  we  were  stalled. 

I  must  add  here  that  my  friend  had  not  yet  dis- 
covered that  I  was  myself  an  electrician.  I  had 
had  no  other  object  in  concealing  the  fact  than 
that,  as  I  had  not  been  asked  my  business,  it  had 
never  been  necessary  for  me  to  declare  it,  and  I 
felt  that  he  would  talk  with  me  more  freely  if  he 
did  not  know  it.  He  knew  that  I  was  an  engineer, 
however,  and  he  attributed  my  ability  to  solve 
certain  questions  which  arose  to  that  fact — to  that 
combined  with  what  he  took  to  be  a  smattering  of 
electricity  which  he  supposed  I  had  acquired  in 
some  way  or  other. 

As  a  matter  of  fact,  however,  I  considered  my- 
self a  full-fledged  electrical  engineer,  and  was,  as 
electrical  engineers  went  in  those  days;  for  besides 
having  had  a  pretty  thorough  training  on  the 
purely  theoretical  side  of  electricity,  I  had  worked 
in  two  of  the  largest  shops  in  the  country  in  all 
the  departments  of  electrical  manufacture.  I 


had  wound  armatures  and  fields,  and  assisted  in 
making  and  dressing  down  all  the  other  parts  of 
machines,  both  large  and  small ;  had  assembled 
these  various  parts,  connected  them  up,  soldered 
the  connections  and  finally  tested  the  completed 
machines.  I  had  also  assisted  in  installing  one 
road  myself,  and  had  inspected  every  road  but 
one  that  was  at  that  time  in  operation  in  the 
country,  so  that  I  was  pretty  familiar  with  electric 
railroad  construction  as  then  developed.  I  knew 
that  my  friend's  experience  had  not  been  nearly  as 
wide  as  my  own,  and  I  was  glad  to  be  with  him  on 
the  occasion  of  the  opening  test  of  this,  which  I 
suspected  was  the  first  road  over  whose  construc- 
tion he  had  been  completely  in  charge. 

Well,  as  I  say,  something  had  happened,  which 
was  only  really  discovered  when  the  attempt  was 
made  to  run  the  car  back.  There  was  a  consider- 
able grade  at  starting,  and  this  the  car  failed  to 
ascend.  We  backed  down  to  the  level  and  tried 
it  again.  The  car  worked  all  right  until  the  grade 
was  reached,  when  she  stopped  again.  This  was 
repeated  a  number  of  times,  and  always  with  the 
same  result.  My  own  experience  made  me  suspect 
at  once  the  true  trouble,  but  it  would  not  do  for 
me  to  suggest.  My  friend  had  been  playing  the 
role  of  a  great  authority  on  electric  railroad  mat- 
ters for  the  special  benefit  of  his  invited  guests  on 
the  car.  He  was  in  very  high  feather,  and  not 
without  reason,  that  night,  because  the  work  of 
his  hands  was  finished,  and  now  he  was  showing 
his  admiring  guests  how  immeasurably  better  it 
worked  than  even  his  own  anticipations  had  led 
him  to  hope. 

For  me  to  have  suggested  the  cause  would  have 
been  considered  a  piece  of  impertinence  of  the 


4  ELECTEIC   RAILWAY   MOTORS. 

highest  order,  not  only  by  him,  but  by  the  other 
guests,  who  looked  upon  my  friend  as  a  wonderful 
man  ;  so  I  kept  quiet. 

My  friend  was  a  man  of  great  self-confidence 
and  equal  to  the  emergency.  In  reply  to  inquir- 
ing glances,  he  said  it  was  due  to  "  something  or 
other  " — using  a  term  not  down  either  in  Web- 
ster's or  Houston's  dictionary — that  it  was  a  very 
trivial  matter  and  could  easily  be  fixed  ;  he  would 
back  down  to  the  level  again  and  fix  it.  He  did 
so — that  is,  he  backed  down,  and,  after  making  an 
examination,  said :  "  Yes,  that's  it,  just  as  I 
thought  ;  the  *  something  or  other '  was  just  what 
caused  the  trouble  ; "  and  he  straightway  pro- 
ceeded to  correct  the  thing.  In  the  meantime 
I  had  had  an  opportunity  of  verifying  my  suspi- 
cions, but  of  course  kept  my  counsel.  When  all 
was  declared  ready  we  entered  the  car  again,  and 
my  friend,  who  really  had  done  nothing,  as  far  as 
I  had  been  able  to  see — he  certainly  hadn't 
touched  the  root  of  the  trouble — turning  on  the 
current  to  the  last  notch,  said,  "  Now  we  go  ; " 
and  we  did  until  we  had  gotten  even  a  little  way 
beyond  the  point  on  the  grade  where  we  had 
always  stalled  before,  and  then  we  stalled  again. 
We  had  gained  a  few  feet  over  previous  attempts 
simply  because  we  had  gained  a  little  more 
momentum  on  the  level.  I  think  my  friend 
understood  this  as  well  as  I,  but  he  pointed  to  the 
small  gain  with  apparent  pride,  and  with  unblush- 
ing assurance  stated  that  that  proved  that  he 
was  right  in  locating  the  trouble,  and  that  now 
he  would  run  back  and  fix  the  thing  for  good. 
We  went  back  and  he  got  under  the  car  again. 
I  watched  him  closely  this  time,  and  after  doing 
absolutely  nothing  more  than  fumble  around  a 


INTRODUCTION.  5 

little  he  came  out  and  announced  that  "  Now  I've 
fixed  her  for  good,  and  I'll  show  you  how  we  can 
mount  that  grade." 

I  have  often  heard  it  claimed  by  horsemen,  and 
have  seen  several  instances  myself  where  good  re- 
sults seemed  to  follow  the  plan,  that  to  start  a 
balky  horse,  the  best  way  is  simply  to  jump  out  of 
the  wagon  and  pretend  to  fix  the  horse's  bridle, 
then  get  in,  and  on  giving  the  signal  the  horse, 
which  neither  whip  nor  oaths  could  budge  before, 
would  start  right  off  as  though  nothing  had 
happened.  This  was  exactly  what  my  friend 
seemed  to  have  done  and  nothing  more,  and  when, 
after  we  had  all  followed  the  injunction  to  get 
"  aboard,"  and  he  commenced  to  turn  on  the  cur- 
rent I  could  not  but  be  astounded  at  the  cheek,  or 
rather  the  assurance,  which  enabled  him  to  keep 
up  the  appearance  of  entire  confidence  in  the  suc- 
cess of  another  attempt  which  he  knew  must  fail 
for  exactly  the  same  reasons  the  others  had.  It  is 
needless  to  state  what  the  result  was,  further  than 
to  say  that  we  did  not  get  quite  as  far  this  time  as 
we  had  before,  and  it  is  also  needless  for  me  to 
state  how,  with  equal  composure,  he  gave  some 
excuse  for  going  back  again  to  the  starting  point. 
I  think  he  said  he  had  forgotten  his  monkey- 
wrench  or  something  else. 

I  determined  this  time  to  speak,  and  when  we 
stopped  at  the  bottom  I  got  off  and  commenced 
looking  around  as  if  hunting  for  something,  and 
stooping  down,  some  distance  from  the  car  so  as 
to  get  him  alone,  cried  out,  "  I've  found  it,"  and,  as 
I  expected,  he  rushed  over,  leaving  the  others  be- 
hind, and  I  whispered, "  Look  at  your  positive  brush 
on  the  front  motor."  He  heard  me  and  under- 
stood. He  stooped  down,  though,  as  if  to  examine 


6  ELECTEIC   RAILWAY   MOTORS. 

what  I  pretended  to  have  found,  and  then,  in  tones 
loud  enough  to  be  heard  by  the  others,  said,  "  No, 
that's  not  it,  but  I've  got  something  that  will  do 
as  well,"  and  lost  no  time  in  getting  under  the  car 
and  repairing  the  broken  connection  which  had 
rendered  useless  one  of  our  motors. 

When  we  got  on  to  the  car  again  and  he  grasped 
the  controlling  switch,  I  know  I  had  more  confi- 
dence that  we  could  ascend  the  grade,  but  his 
appearance  betrayed  not  one  whit  more  than  it  had 
on  the  two  previous  attempts.  As  for  the  other 
parties,  I  am  sure  there  was  never  a  suspicion. 
We  completed  the  return  trip  in  great  shape,  and 
the  trial  trip  was  pronounced  a  success,  and  my 
friend  was  the  hero  of  the  hour.  We  returned  to 
the  car  barns,  and  after  he  had  seen  everything 
safe  for  the  night  we  walked  home  together.  He 
seemed  buried  in  deep  thought  for  some  distance, 
but  finally  broke  the  silence  by,  "You  played  me 
a  darned  mean  trick."  I  was  very  much  surprised 
at  his  attitude,  thinking  that  he  should  rather 
have  thanked  me  for  helping  him  out  of  his  diffi- 
culty. I  knew  that  he  would  have  found  the 
difficulty  after  a  while  if  left  to  his  own  resources, 
but  thought  I  had  saved  him  some  embarrassment 
which  further  delay  might  have  caused  him,  so 
I  laughingly  asked,  "  How  ?  "  to  which  he  replied  : 
"  By  not  letting  me  know  before  that  you  were  an 
electrician." 

The  above  anecdote  is  related  now  merely  to 
show  how  a  little  bravado,  judiciously  used,  may 
save  a  reputation  where  entire  candor  would  have 
been  fatal.  However  reprehensible  this  practice 
may  be  in  the  abstract,  it  is  one  that  pervades  all 
walks  in  life,  and  is  nowhere  more  prevalent,  per- 
haps, than  in  the  medical  profession.  It  is,  in  fact, 


INTRODUCTION.  7 

often  used  there  to  advantage,  for  if  the  physician 
should  fail  to  inspire  his  patient  with  confidence  in 
the  beginning,  it  would  be  almost  impossible  for 
him  to  succeed  later,  and  it  is  conceded  that  confi- 
dence in  one's  physician,  as  well  as  in  the  remedies 
one  takes,  is  of  the  greatest  help  in  curing  disease. 

If  we  find  this  practice  so  general  in  such  an 
honorable  profession  as  medicine,  it  is  not  surpris- 
ing if  we  find  it  among  the  motormen,  nor  can  we 
disparage  it  there  while  we  uphold  it  elsewhere. 
In  fact,  I  believe  the  motorman  or  electrical  artisan 
is  really  less  to  blame  than  many  others  by  the 
circumstances  of  his  position.  Most  often  the 
electric  motorman  has  obtained  his  position  as  a 
reward  for  faithful  services  as  a  driver  or  con- 
ductor of  a  horse  car.  In  his  previous  occupation 
his  hours  have  been  long  and  his  work  exhausting 
both  to  mind  and  body,  and  when  his  day's  work 
is  done  he  is  in  no  condition  for  study  or  more 
work.  Besides,  as  a  driver,  he  has  probably  mas- 
tered his  business,  and  there  has  been  no  incentive 
to  further  study. 

With  this  habit  of  mind  he  is  transferred  with- 
out  any  special  preparation  to  the  responsibilities 
of  the  care  of  the  electrical  equipment  of  his  car. 
He  is  broken  in  by  someone  who  has  had  a  little 
more  experience  than  he  has  had,  and  after  having 
been  shown  the  various  parts  of  his  apparatus, 
and  how  they  are  intended  to  operate,  is  given  a 
set  of  rules  whicli  tell  him  that  he  must  do  this 
and  must  not  do  that,  and  is  allowed  then  to  shift 
for  himself.  He  is  expected  to  talk  about  a  cur- 
rent which  he  can't  see,  and  to  guard  against 
results  which  he  knows  only  by  name.  A  new 
language  is  placed  in  his  mouth  which  he'  does 
not  understand,  but  which  he  understands  some- 


8  ELECTRIC   RAILWAY   MOTORS. 

how  is  intimately  connected  with  his  business. 
His  hours  are  no  shorter  than  before,  and  books 
which  would  explain  matters  are  too  expensive, 
even  if  he  had  time  to  read  them,  or  entirely  inac- 
cessible. His  companion  motormen  are  using  this 
new  language  familiarly,  and  he  soon  acquires 
that  habit  almost  unconsciously,  and  as  soon  as  he 
is  thus  initiated  into  the  charmed  circle  which 
speaks  this  foreign  language  he  becomes  with  his 
brother  motormen  a  class  distinct  from  that  class 
from  which  they  have  all  sprung.  If  he  knows 
little  of  electricity,  he  still  knows  more  than  his 
former  companions,  and  they  treat  him  with  a 
respect  due  to  his  superior  knowledge.  It  will 
not  do  for  him  to  admit  ignorance,  and  he  has  an 
answer  ready  for  every  question.  Nor  does  he 
care  to  show  his  ignorance  among  his  companions 
by  asking  them  questions  or  by  asking  questions 
of  others  in  their  presence,  and  in  this  way  too 
often  stands  in  his  own  light.  That  the  average 
motorman  is  anxious  to  inform  himself,  when  he 
can  do  so  under  circumstances  which  are  not  em- 
barrassing, I  know  well  from  personal  experience, 
for  I  have  had  individuals  ply  me  with  questions, 
when  they  could  get  me  alone,  who  would  rather 
have  died  almost  than  to  have  asked  the  same  ques- 
tions in  the  presence  of  fellow- workmen. 

No  one  blames  them  for  this.  It  is  human 
nature,  and,  as  I  have  stated  before,  they  have 
shining  examples  in  the  same  practice  in  members 
of  professions  considered  more  dignified  than 
theirs. 


CHAPTER  II. 

TECHNICAL   TEKMS,   ETC. 

WHENEVER  we  undertake  the  study  of  a  new 
subject,  it  becomes  necessary  to,  in  a  measure, 
break  away  from  old  things — old  thoughts,  old 
names,  old  tools,  and  oftentimes  accustomed 
methods,  and  to  adopt  in  their  place  new  ones 
which  those  who  have  had  experience  in  the  sub- 
ject have  found  more  suited  to  the  new.  It  is 
this  first  breaking  away  from  the  old  and  accus- 
toming ourselves  to  the  new  that  is  the  greatest 
stumbling-block  in  the  path  of  the  student.  We 
can  best  describe  a  phenomenon  or  a  thing  to 
a  person  unfamiliar  with  it  by  likening  it  to  some- 
thing with  which  he  is  familiar,  and  then,  after 
conveying  to  his  mind  a  clear  idea  of  how  the 
new  resembles  the  old,  impress  upon  his  mind  as 
well  as  we  can  that  the  resemblance  is  not  com- 
plete, and  that  the  manner  in  which  the  familiar 
differs  from  the  unfamiliar  is  really  the  essential 
difference  between  the  two — we  cannot  at  first 
explain  this  difference  clearly  ;  he  must  take  that 
much  on  faith  and  assume  at  the  outset  that  what 
is  said  is  true.  As  the  student  becomes  more  and 
more  familiar  with  the  thing  described,  by  han- 
dling it  and  seeing  it  used,  he  will  begin  to  appre- 
ciate more  fully  its  nature,  and  the  peculiarities 
of  the  new  object  itself.  It  is,  therefore,  well 
in  the  beginning  to  substitute  for  the  new  thing 


10  ELECTRIC   RAILWAY   MOTORS. 

an  entirely  new  name  instead  of  continuing  to 
describe  it  by  the  names  of  things  which  it  partly 
resembles,  so  that  the  mind  may  associate  with 
the  new  name  the  actual  qualities  of  the  new 
thing  rather  than  be  misled  by  the  name  which 
the  resemblance  would  indicate.  This  is  true  of 
all  sciences,  and  it  is  true  of  electricity.  Each 
branch  of  science  presents  some  phenomena  pe- 
culiar to  itself,  and  therefore  must Jiave  names  for 
them,  and  it  is  the  names  peculiar  to  this  science 
that  constitute  its  technical  terms.  If  a  branch  of 
science  which  we  are  about  to  take  up  is  full  of 
phenomena  new  to  us,  it  will  be  full  of  strange 
names,  and  it  is  the  mastery  of  these  that  is  most 
formidable  to  us,  for  the  meaning  of  each  sentence 
is  or  may  be  obscured  by  their  presence.  It  is 
frequently  said  that  scientific  men  delight  in 
obscuring  their  meaning  behind  technical  terms, 
whereas  the  fact  is  they  are  using  that  language 
which  is  most  intelligible  to  them,  and  is  only 
unintelligible  to  us  because  of  our  ignorance  of 
the  subject. 

If  the  student  could  only  appreciate  the  fact 
that  technical  language  is  really  the  simplest  and 
most  direct  that  can  be  used,  much  of  the  difficulty 
of  the  subject  at  the  outset  would  be  removed,  and 
it  is  therefore  deemed  wise  to  add  a  few  words 
here  with  the  hope  of  impressing  upon  his  mind 
the  truth  of  this  statement. 

In  our  everyday  life  we  are  constantly  making 
use  of  technical  terms  as  a  matter  of  convenience; 
we  do  it  unconsciously,  it  is  true,  but  are  im- 
pelled to  it  by  the  same  necessities  as  is  the  elec- 
trician, the  geologist  or  the  astronomer.  As  an  illus- 
tration, suppose  we  were  to  try  to  describe  a  dog 
to  a  person  who  had  never  seen  one,  or  any  animal 


TECHNICAL  TERMS,  ETC.  11 

of  that  "family.  We  would  have  to  describe  it  in 
some  such  vague  terms  as  this :  that  it  had  four 
legs  and  a  tail,  was  covered  with  hair,  made  a 
peculiar  noise  when  angry  or  excited  (imitating  its 
bark),  ate  meat  as  its  chief  food,  etc.,  etc,  rehears- 
ing many  of  its  characteristics,  which,  however 
well  described,  would  apply  equally  well  to  some 
other  animal.  Supposing,  after  having  failed  to 
convey  in  this  way  any  adequate  idea  of  the  ani- 
mal, we  should  secure  a  specimen  and  tell  him  that 
that  was  a  dog ;  the  story  would  be  told  a  great 
deal  better,  and  ever  after  the  technical  term  "  dog  " 
would  have  a  definite  meaning  to  him — a  much 
more  definite  meaning  than  any  description  that 
we  could  give.  If  his  education  stopped  there — if 
he  had  seen  but  one  breed  of  dog,  and  perhaps  but 
a  single  specimen,  all  dogs  to  his  mind  would  be 
about  the  same.  .  If  the  one  examined  had  been  a 
great,  shaggy-haired  Newfoundland,  he  would  not 
recognize  in  the  hairless  Mexican  dog  an  animal  of 
the  same  family  at  all;  so  that  even  after  he  had 
seen  a  dog  of  one  breed  it  would  be  almost  as  diffi- 
cult to  describe  to  him  another  of  a  different  breed 
as  it  was  in  the  first  place  to  tell  him  what  kind 
of  an  animal  a  dog  of  any  kind  was.  On  the  other 
hand,  among  dog  fanciers  how  definite  the  phrase 
"Irish  setter"  is,  for  instance.  Those  two  words 
— that  technical  phrase — convey  to  the  mind  more 
definite  information  than  could  be  imparted  in 
pages  of  printed  matter,  or  perhaps  more  than  in 
hours  of  discourse.  To  the  person  who  was  very 
familiar  with  dogs  it  would  give  an  idea  not  only 
of  the  size  and  color,  but  of  the  general  character, 
and  yet  how  meaningless  it  would  be  to  one  who 
was  not  familiar  with  the  term.  To  him  it  would 
not  even  convey  the  idea  of  a  dog  of  any  kind. 

^^eSE    L!BR^J>^ 

f  CFTHE         ^^       \ 

(UNIVERSITY) 
^.  OF  ; 


12  ELECTRIC   RAILWAY   MOTORS. 

Thus  it  is  that  a  technical  term  only  has  a  mean- 
ing for  us  as  we  associate  with  it  certain  ideas. 
It  seldom  describes  the  thing  itself,  for  it  is  im- 
possible, as  we  have  shown,  to  fully  describe  to 
another  something  he  has  never  seen.  The  best 
we  can  do  is  to  liken  it  to  something  that  he  has 
seen,  and  then  caution  him  that  the  likeness  is  not 
exact.  So  that  in  describing  electrical  phenomena 
it  must  be  understood  that  while  our  explanations 
and  descriptions  are  the  best  we  can  give,  they  are 
not  always  exact,  but  only  approximately  true. 

It  will  be  apparent  to  everyone  that  there  is 
more  power  available  in  a  waterfall  in  which  the 
volume  or  quantity  of  water  flowing  is  great  than 
in  one  where  the  quantity  is  small,  and  that  the 
amount  of  power  will  be  still  greater  if  the  water 
falls  a  great  distance  than  if  it  falls  but  a  short 
distance.  In  describing  a  waterfall,  therefore,  it 
is  not  sufficient  to  state  either  that  it  is  of  great 
height  or  that  it  is  of  great  volume.  We  must 
state  both  the  height  and  the  volume.  It  is  not 
sufficient  to  say  that  a  waterfall  is  five  hundred 
feet  high,  or  that  the  water  flows  at  the  rate  of 
one  thousand  gallons  per  second,  but  when  it  is 
said  that  a  stream  falls  over  a  precipice  five  hun- 
dred feet  high,  at  the  rate  of  one  thousand  gallons 
per  second,  we  know  exactly  how  large  the  fall  is 
and  can  figure  out  just  how  many  horse  power  can 
be  developed.  Electricity  is  most  often  likened  to 
a  stream  of  water  falling  over  a  precipice,  and  the 
energy  of  an  electric  current  is  described  in  ex- 
actly the  same  way,  only  instead  of  measuring  the 
height  of  its  fall  in  feet,  as  we  usually  do  water, 
electricians  have  decided  to  use  the  term  "  volt," 
and  instead  of  measuring  the  flow  in  gallons  per 
second  they  measure  it  in  "  amperes." 


TECHNICAL   TERMS,    ETC.  13 

It  is  not  necessary  at  this  point  to  state  just  how 
much  a  volt  or  an  ampere  is — the  terms  are  mean- 
ingless in  themselves,  and  are  the  names  of  men 
who  early  did  much  to  advance  the  science  of 
electricity,  that  is  all  ;  but  we  must  now  try  to 
give  them  a  meaning.  Using  these  terms  in  the 
above  example,  the  waterfall  would  be  described 
as  falling  five  hundred  volts  at  a  rate  of  one 
thousand  amperes.  Perhaps  we  would  better 
represent  the  volt  as  the  equivalent  of  a  pound  of 
pressure,  and  then  we  can  say  of  the  water  in  a 
water  pipe  that  it  flows  at  the  rate  of  so  many 
amperes  at  a  pressure  of  so  many  volts. 

Now,  for  our  purposes,  we  may  consider  the 
trolley  and  feed  wires  as  copper  pipes  conveying 
water  from  a  pump  at  the  power  station  to  a  tur- 
bine or  other  water  wheel  beneath  the  car.  The 
pressure  of  the  water  in  this  pipe  is  kept  by  the 
pump  at  five  hundred  pounds,  and  more  or  less 
gallons  of  it  per  second  are  used  on  the  motor  as 
we  turn  the  controlling  lever  (faucet)  on  or  off. 

Everyone  knows  that  if  we  twirl  a  wheel  on  an 
axle,  be  it  ever  so  well  greased,  it  will  stop  before 
long  unless  we  continue  applying  power.  It  stops 
by  reason  of  friction.  Every  carman  also  knows 
that,  if  his  journals  are  not  kept  well  greased,  his 
car  will  pull  harder  and  he  will  get  a  hot  box. 
This  is  because  there  is  more  friction  and  the  heat 
is  generated  faster  than  the  rubbing  parts  can  be 
cooled  off,  and  therefore  it  accumulates  to  such  an 
extent  as  to  become  not  only  apparent,  but  often- 
times troublesome.  Now  water,  in  flowing  through 
a  pipe,  be  it  ever  so  smooth,  encounters  friction 
against  the  inside  of  the  pipe.  Heat  is  not  ob- 
served in  the  case  of  water  friction,  because  the 
water  carries  it  away  so  rapidly,  but  the  main 


14  ELECTEIC    RAILWAY    MOTORS. 

effect  is  to  retard  the  flow  of  water.  Thus  un- 
der a  given  pressure  a  pipe  of  a  given  size,  say 
one  hundred  feet  long,  will  deliver  much  more 
water  per  second  than  it  will  if  the  pipe  were  a  mile 
or  two  long  ;  and  again,  more  water  will  be  deliv- 
ered through  a  smooth  pipe  than  through  an  equal 
length  of  a  rough  or  rusty  pipe,  for  the  same  rea- 
son that  in  the  former  there  is  less  friction. 

Now  in  the  electric  current  we  have  pretty 
much  the  same  state  of  affairs.  Every  conductor, 
however  good,  offers  some  resistance,  in  the  way 
of  friction,  to  the  flow  of  current,  and  of  two  wires 
of  the  same  diameter  that  will  offer  the  greatest 
resistance  which  is  longest.  If  one  wire  be  twice 
as  long  as  another,  it  will  offer  just  twice  the  re- 
sistance, and  that  which  is  the  smoothest  inside, 
or  in  other  words  the  best  conductor,  will  offer  the 
least  resistance.  Copper  is  the  best  conductor  of 
electricity  we  have  (except  silver),  and  therefore 
our  copper  feeder  wires  and  trolley  wires  may  be 
likened  to  polished  metallic  pipes  carrying  water 
from  our  pump  to  our  water  wheel  (motor)  under 
the  car,  and  the  poorer  conductors,  such  as  iron  or 
brass  or  zinc,  may  be  likened  to  rusty  pipes  which 
produce  more  friction  than  the  copper  ones  do. 
But  the  electric  current  cannot  carry  off  heat  in 
the  same  manner  that  water  does,  so,  as  in  the 
case  of  the  car  axle,  if  the  conductor  be  over- 
worked it  will  get  hot.  Electricians  have  a  way 
of  measuring  the  resistance  to  the  flow  of  current 
in  conductors  and  express  this  resistance  in 
"  ohms."  The  word  "  ohm,"  like  volt  and  ampere, 
has  no  meaning  in  itself,  and  is  also  the  name  of 
an  early  investigator,  but  to  the  electrician,  who 
uses  it  to  express  the  resistance  due  to  friction,  it 
has  a  definite  meaning.  Thus  we  have  the  three 


TECHNICAL   TERMS,  ETC.  15 

fundamental  units  of  electricity  :  the  volt,  equiv- 
alent to  a  water  pressure  of  say  a  pound  to  the 
square  inch,  or  to  a  head  of  water  of  say  one  foot  ; 
the  ampere,  equivalent  to  a  rate  of  flow  of  water 
of  so  many  gallons  per  second  or  minute  ;  and  the 
ohm  as  the  unit  of  resistance  to  a  flow  of  water  in 
a  pipe,  which  for  present  purposes  we  may  con- 
sider our  conductors  to  be.  We  must  bear  in 
mind  that  as  there  are  all  sorts  of  pipes  for  con- 
veying water — large  ones,  small  ones,  smooth  and 
polished  ones  and  rusty  ones,  all  of  which  differ 
in  the  amount  of  water  which  they  will  deliver 
under  a  given  pressure  in  a  second  or  minute,  ac- 
cording as  they  offer  more  or  less  frictional  resist- 
ance to  its  flow — so  are  there  different  kinds  of 
electrical  pipes  or  conductors,  which  likewise  differ 
in  their  carrying  capacity  of  the  electric  current 
as  they  are  large  or  small,  smooth  and  polished 
(good  conductors,  silver,  copper)  or  rusty  ones 
(poor  conductors,  iron,  brass,  zinc,  carbon,  etc.); 
and  although  all  of  these  units  bear  strange  names 
— names  of  men  who  have  distinguished  them- 
selves in  scientific  research — they  are  very  closely 
equivalent  to  other  units  with  which  we  have  long 
been  familiar 


CHAPTER  III. 

OHM'S  LAW. 

THESE  three  units  bear  a  definite  relation  to 
each  other  also.  Although  common  sense  would 
seem  to  tell  us  that  with  a  given  pressure  more 
water  would  be  delivered  through  a  short  pipe  in 
a  given  time  than  through  a  long  one  of  the  same 
diameter  ;  that  of  two  pipes  of  the  same  size  and 
length  that  which  was  smooth  inside  would  deliver 
more  water  in  a  given  time  than  that  which  was 
rough  or  rusty  or  partly  obstructed,  and  that  of 
two  pipes  of  the  same  kind,  either  smooth  or  rusty 
inside,  that  would  deliver  the  greater  quantity 
of  water  which  was  of  the  greater  diameter — al- 
though, as  I  say,  common  sense  would  seem  to  tell 
us  all  this,  electricians  were  a  long  time  in  finding 
out  that  it  was  true  for  electricity  as  well  as  for 
water. 

It  was  George  Simon  Ohm  who  first  discovered 
this  simple  relation  of  the  flow  of  a  current  of 
electricity,  but  when  he  announced  that  the  amount 
of  current  that  would  flow  through  any  conductor 
was  equal  to  the  pressure  (volts)  divided  by  the 
frictional  resistance  (ohms),  although  he  had  really 
only  stated  that  the  electric  current  obeyed  the 
same  laws  essentially  as  the  flow  of  water  through 
pipes,  there  were  few  who  believed  that  it  was 
true.  Other  investigators  had  imagined  that  the 
relation  between  the  flow  and  the  pressure  and 

16 


17 

resistance  was  a  much  more  complex  one,  and  had 
gotten  up  long  mathematical  formulae  to  express 
this  supposed  relation.  Ohm's  law,  as  it  soon 
became  called,  was  entirely  too  simple  for  them, 
and  for  a  long  time  they  would  not  accept  it. 
Further  experiment  fortunately  proved  it  to  be 
strictly  true,  and  this  law,  which  is  that  the  rate 
of  flow  of  an  electric  current  through  a  con- 
ductor, or  the  amperes,  is  equal  to  the  pressure,  or 
electromotive  force  or  volts  (all  of  which  terms 
mean  the  same  thing),  divided  by  the  resistance, 
or  ohms,  has  become  the  very  foundation  of  the 
science  of  electricity.  It  is  usually  written  : 
Electromotive  force 

Current— , 

Resistance 

or,  for  the  sake  of  brevity,  the  initial  letters  are 
used  only  and  the  expression  becomes: 

E 
C=— . 

ft 

Nothing  could  be  simpler  than  this  when  one 
understands  it,  and  yet  those  who  do  not  know 
any  better  imagine  that  the  science  of  electricity 
is  an  exceedingly  abstruse  one.  The  contrary  is 
really  the  fact,  but  unless  one  understands  the 
A  B  C's  he  cannot  read.  It  is  worth  while,  there- 
fore, that  we  devote  some  time  in  making  Ohm's 
law  entirely  clear,  for  upon  it  is  constructed  prac- 
tically the  whole  of  the  science  with  which  we 
have  to  deal.  The  three  letters 

E 
C=— 

R 

(amperes  equals  the  volts  divided  by  the  resistance 
or  ohms)  constitutes   the  whole  alphabet  of   our 


18  ELECTRIC   RAILWAY   MOTOKS. 

science,  and  we  only  need  to  know  how  to  use 
these  letters  to  solve  any  electrical  problem  with 
which  we  are  confronted. 

Let  us  illustrate  the  use  of  this  law  by  a  few 
numerical  examples.  Scientific  men  have  very 
carefully  determined  the  resistance  in  ohms  of 
different  sizes  of  pure  copper  wire,  and  have  found 
that  at  the  ordinary  temperature  a  No.  10  B  and 
S  wire,  which  is  a  trifle  over  -fa  inch  in  diameter, 
offers  a  resistance  of  a  trifle  over  1  ohm  per 
thousand  feet.  (The  exact  figures  are  iWjftftr 
inch  in  diameter  and  ITH$TT  °hm  resistance 
per  thousand  feet.)  Let  us  discard  the  fractions 
and  use  the  whole  numbers.  If  we  were  designing 
a  dynamo  or  buying  one,  we  could  obtain  one  that 
would  give  us  any  voltage  we  desired.  In  street 
railway  practice  a  pressure  of  500  volts  or  there- 
abouts is  always  used,  and  we  will  assume  that  we 
have  a  dynamo  that  will  generate  that  pressure, 
and  we  have  a  circuit  of  No.  10  B  and  S  wire  of 
10,000  feet,  and  we  desire  to  know  what  rate  of 
flow  (how  many  amperes)  can  be  sent  over  that 
circuit. 

One  thousand  feet  of  No.  10  wire  offer  a  resist- 
ance of  1  ohm  ;  10,000  feet  will  therefore  offer  a 
resistance  of  10X1,  or  10  ohms.  The  voltage  or 
electromotive  force  at  our  disposal  is  500.  Ohm's 
law  says  that  the  current  that  will  flow  will  be 
equal  to  the  voltage  or  electromotive  (in  this  case 
500)  divided  by  the  resistance  (in  this  case  10 
ohms),  and  therefore  the  answer  is  that  C  (or 
amperes)  =  *f£,  or  50  amperes.  Now  if  we  should 
make  our  circuit  twice  as  long,  or  20,000  feet,  the 
resistance  would  be  just  twice  as  great  (20X1  = 
20)  and  our  equation  would  be  C  —  5g°/  =  25.  That 
is  to  say,  with  the  same  size  wire  of  double  the 


19 

length  the  rate  of  flow  of  current  would  be  only 
half  as  great,  or  25  amperes  instead  of  50  amperes. 
In  the  same  way  we  find  that  if  our  circuit  were 
only  half  as  long,  or  5000  feet,  the  resistance 
being  also  cut  in  two,  the  flow  of  current  would 
be  twice  as  great,  or  100  amperes.  Now  if  we 
double  the  amount  of  copper — that  is,  use  two  No. 
10  wires  instead  of  one — each  of  these  will  carry 
the  same  amount  of  current,  and  at  10,000  feet 
could  deliver  2X50  amperes,  or  100  amperes. 
That  is  to  say,  if  we  double  the  weight  of  our 
copper,  either  by  using  two  wires  of  the  same 
size  or  a  single  one  of  the  same  weight  as  the  two 
combined,  we  will  reduce  our  resistance  by  half, 
and  consequently  be  enabled  to  deliver  twice  as 
much  current  at  the  same  distance. 

But  supposing  we  have  other  data  given.  Sup- 
pose it  is  required  to  determine  what  sized  wire 
to  use  to  transmit  say  1000  amperes  to  a  distance 
of  20,000  feet — the  electromotive  force  being,  as 
before,  500  volts.  Referring  to  Ohm's  law 

E 

C=— 
R 

we  have  C,  the  amperes,  equals  1000,  and  E,  the 
pressure  or  electromotive  force,  is  500.  Substitut- 
ing these  in  the  equation,  it  becomes 

500 

1000= . 

R 

By  simple   arithmetic  this   may  be  changed  to 

500 

1000  R=500  andR= =%. 

1000 

Thus  we  find  that  the  resistance  of  the  conductor 
in  ohms  for  20,000  feet  is  J.  The  resistance  of 


20  ELECTRIC    RAILWAY    MOTORS. 

this  same  wire  per  1000  feet  will  be  -g1^  of  J,  or  -fa 
ohm.  A  No.  10  wire  has  a  resistance  of  1  ohin 
per  1000  feet,  and  the  required  wire,  which  has  a 
resistance  of  but  fa  ohm  per  1000  feet,  must  be 
forty  times  as  heavy  as  a  No.  10  wire,  or  equivalent 
to  40  No.  10  wires,  which  by  reference  to  any 
wiring  table  will  be  found  to  be  equal  to  two  0000 
wires. 

Or  supposing  we  have  our  wire  already  strung — 
say  a  No.  10  wire — and  must  deliver  1000  amperes 
over  a  circuit  20,000  feet  in  length,  what  electro- 
motive force  must  we  use  ? 

The  resistance  of  1000  feet  of  No.  10  wire  is 
1  ohm.  The  resistance  of  20,000  feet  will  be 
20X1  ohms.  The  amperes  or  current  which  we 
have  to  deliver  is  1000.  By  Ohm's  law 

E 

C=— 
R 

Substituting  for  C  its  value  1000  and  for  R  its 
value  20,  our  equation  becomes 

E 

1000=—. 
20 

or  by  simple  arithmetic  20,000 =E,  which  is  to 
say  that  the  electromotive  force  will  have  to  be 
20,000  volts  to  force  a  current  of  1000  amperes 
around  a  circuit  of  20,000  feet  of  No.  10  wire. 

Examples  have  now  been  given  of  all  possible 
cases  of  wire  calculation  in  their  simplest  form, 
and  these  illustrate  the  way  in  which  Ohm's  law 
is  used  in  electrical  calculations.  Of  course  others 
may  and  usually  do  arise  in  which  some  compli- 
cations are  introduced — for  instance,  it  is  usually 
required  not  simply  to  determine  what  is  the  small- 
est wire  that  can  possibly  carry  a  given  number  of 


OHMS 


amperes  a  certain  distance,  but  to  determine  what 
pize  wire  will  carry  that  current  the  required  dis- 
tance with  a  given  drop  or  loss  of  potential  or 
electromotive  force  or  pressure;  but  we  will  not 
discuss  that  question  now,  merely  passing  it  by 
with  the  statement  that  it  is  a  very  simple  matter 
to  do,  and  requires  no  more  knowledge  of  arith- 
metic than  is  involved  in  the  examples  already 
given. 

It  is  strongly  urged  upon  all  who  are  not  famil- 
iar with  the  use  of  Ohm's  law,  and  who  wish  to  de- 
rive benefit  from  the  succeeding  articles,  to  work 
out  these  problems  over  and  over  again  until  they 
are  thoroughly  familiar  with  the  use  of  the  law,  for, 
as  before  stated,  it  is  the  key  to  the  whole  science 
of  electricity.  It  will  be  observed  that  in  Ohm's 
law  there  are  three  elements  involved,  viz.,  the 
pressure  or  electromotive  force  or  voltage,  which- 
ever we  choose  to  call  it,  the  rate  of  flow  of  the 
current,  or  amperes,  and  the  resistance  which 
that  flow  encounters  in  the  conductors,  which  is 
measured  in  ohms.  These  same  three  elements 
are  involved  in  the  flow  of  all  other  fluids  as  well, 
but  are  simply  disguised  under  different  names. 
As  before  stated,  the  flow  of  water  in  pipes  in- 
volves pressure  (usually  measured  in  pounds  per 
square  inch  or  head  in  feet,  corresponding  to 
volts  in  electric  currents),  rate  of  flow  (usually 
measured  in  gallons  or  barrels  or  cubic  feet  per 
minute  or  second,  corresponding  to  amperes)  and 
frictional  resistance  (usually  measured  in  loss  of 
feet  or  inches  in  head  or  in  pounds  pressure, 
corresponding  to  ohms  in  electricity),  and,  as 
shown  by  the  examples,  if  any  two  of  these 
three  elements  are  given,  the  third  may  be  de- 
termined. 


22  ELECTRIC    RAILWAY    MOTORS. 


RATE    OF    WORK. 

In  mechanics  we  say  that  when  energy  is 
expended  at  such  a  rate  as  to  lift  a  weight  of  1 
pound  1  foot  in  1  second  it  is  doing  work  at  the  rate 
of  1  foot  pound  per  second,  and  when  it  is  doing 
an  amount  of  work  equivalent  to  raising  550 
pounds  1  foot  high  per  second,  or,  what  is  the 
same  thing,  raising  33,000  pounds  1  foot  high  per 
minute,  the  work  done  is  equal  to  1  horse  power. 
A  mechanical  horse  power 'is  therefore  defined  as 
that  expenditure  of  energy  which  will  raise  a 
weight  of  550  pounds  1  foot  high  in  1  second,  or 
33,000  pounds  (60X550)  1  foot  high  in  1  minute. 

Since  the  raising  of  a  weight  usually  conveys  to 
our  minds  the  idea  of  a  lift  or  pull,  rather  than  of 
a  pressure,  and  we  have  heretofore  been  speaking 
only  of  pressures,  it  may  be  well,  in  order  to  make 
clear  the  exact  similarity  between  the  mechanical 
and  electrical  units  of  work  to  translate  the  "  pull " 
or  "lift"  into  a  pressure.  That  "pull"  and 
"  pressure  "  are  really  equivalent  will  be  apparent 
from  a  familiar  example.  When  it  is  desired  to 
move  a  car  in  the  barns  it  is  immaterial  whether 
we  get  behind  and  push  or  get  in  front  and  pull. 
One  method  may  be  more  convenient  than  the 
other,  but  the  amount  of  work  done  in  either  case 
if  the  car  be  moved  the  same  distance  in  the  same 
time  will  be  exactly  the  same,  and  if  the  work 
thus  performed  is  the  same  as  that  required  to 
lift  or  press  upward  a  weight  of  550  pounds 
through  a  height  of  1  foot  in  1  second  it  will 
be  exactly  a  mechanical  horse  power.  Thus  we 
see  that  in  the  measure  of  rate  of  mechanical  work 
which  we  call  the  horse  power  four  elements  are 
involved^  viz.,  pressure,  weight  or  quantity,  dis- 


BATE    OF   WOBK.  23 

tance  and  the  time  occupied  in  lifting  or  pushing 
the  given  weight  or  quantity  through  that  distance. 
Now  in  electrical  language  it  will  be  remem- 
bered that  the  volt  or  electromotive  force  has  been 
defined  as  the  equivalent  of  mechanical  pressure. 
We  might  also  now  say  that  it  is  the  equivalent 
of  mechanical  pull  or  lift.  We  have  denned  the 
ampere  as  a  rate  of  flow  of  current  and  likened  it 
to  the  flow  of  so  many  gallons  of  water  per  second. 
While  electricity  is  not  supposed  to  have  weight, 
we  may  for  present  purposes  suppose  that  it  has. 
A  gallon  of  water  weighs  about  8  pounds,  and  if 
it  is  lifted  through  1  foot  in  1  second,  8  foot 
pounds  of  work  will  have  been  done.  If  we  lift  it 
or  push  it  so  fast  that-  in  1  second  we  have  lifted 
it  through -S-f  ^— 68  j-  feet  in  one  second  instead,  we 
will  have  done  work  equivalent  to  550  foot  pounds 
in  1  second,  which  is  equivalent  to  1  horse  power. 
Therefore,  since  the  ampere  is  a  similiar  electrical 
expression  to  the  mechanical  expression  of  a  flow 
of  so  many  gallons  per  minute,  and  since  the  volt 
is  equivalent  to  the  mechanical  expression  of  so 
many  pounds  pressure,  and  the  product  of  pressure 
into  gallons  per  second  gives  us  foot  pounds  per 
second,  550  of  which  make  a  mechanical  horse 
power,  we  ought  to  expect  that  the  product  of 
electrical  pressure  (the  volts)  into  the  rate  of  flow 
of  the  electrical  currents  (the  ampere)  would  give 
us  something  similar  to  the  foot  pound  per  second, 
and  that  a  certain  number  of  these  would  be 
equivalent  to  a  mechanical  horse  power,  and  so  it 
is.  If  we  have  an  electric  current  of  1  ampere 
flowing  under  a  pressure  of  1  volt,  we  have  elec- 
trical energy  expended  at  the  rate  of  1  watt, 
and  this  unit  is  of  such  a  size  that  746  of  them 
are  equivalent  to  1  mechanical  horse  power.  Or 


24  ELECTRIC   RAILWAY   MOTORS. 

in  other  words,  if  746  amperes  under  1  volt  pres- 
sure, or  1  ampere  under  746  volts  pressure,  be 
wholly  expended  on  an  electric  motor,  that  motor 
will  be  capable  of  lifting  a  weight  of  550  pounds 
1  foot  high  in  1  second,  or  1  pound  550  feet 
high  in  the  same  time,  or  33,000  pounds  1  foot 
high  in  a  minute,  or  will  be  equivalent  to  a  horse 
power.  Thus  while  the  watt  is  not  exactly  the 
same  thing  as  a  foot  pound  per  second,  it  is  a  unit 
of  exactly  the  same  kind,  but  of  a  different  size, 
just  as  although  an  ounce  is  not  the  same  thing  as 
a  pound,  it  is  a  unit  of  the  same  kind.  But  746 
watts  are  exactly  the  same  thing  as  a -horse  power, 
just  as  16  ounces  are  the  same  thing  as  a  pound. 

Thus  we  have  the  electrical  unit  of  rate  of  work 
or  expenditure  of  energy  also  named  after  a  distin- 
guished early  investigator,  and  it  has  no  meaning 
whatever  except  that  which  electricians  have 
assigned  to  it  as  described.  The  watt  is  equivalent 
to  TJ-g-  of  a  horse  power,  and  the  foot  pound  per 
second  is  -§^-5-  of  a  horse  power,  so  that  the  watt  is 
somewhat  smaller  than  the  foot  pound  per  second  ; 
but  the  electrical  horse  power  and  the  mechanical 
horse  power  are  exactly  the  same  thing.  The  watt 
is  also  sometimes  called  the  volt-ampere,  because 
it  is  obtained  by  multiplying  the  volt  by  the 
ampere.  The  kilowatt  is  merely  a  thousand  watts, 
the  word  kilo  meaning  thousand.  Since  746  watts 
equal  a  horse  power,  a  kilowatt  is  equal  to  *f££-, 
which  is  equal  to  nearly  1 J  horse  power. 

EXAMPLES. 

How  many  electrical  horse  power  can  be  deliv- 
ered over  a  No.  10  wire  whose  length  is  20,000 
feet,  the  electromotive  force  being  500  volts? 

Ans. — The  resistance  of  No.  10  wire  is  1  ohm 


EXAMPLES.  25 

per  1000  feet.  The  resistance  of  20,000  feet  will 
therefore  be  20  ohms.  According  to  Ohm's  law 

E 

C=—  . 
R 

According  to  the  problem  the  electromotive  force 
or  E=500,  and  the  resistance  orR=20.  Substi- 
tuting these  in  the  equation,  it  becomes  C  =-8^=  25. 
That  is  to  say  that  25  amperes  can  be  delivered 
over  20,000  feet  of  No.  10  wire  if  the  pressure  is 
500  volts. 

The  watts  delivered  will  be  equal  to  the  electro- 
motive force  multiplied  by  the  current  in  amperes, 
or  25X500=125,000  watts.  Since  746  watts 
equal  1  horse  power,  the  horse  power  delivered 
will  be  J-|f  $£=lfrff£  horse  power. 


The  current  passing  over  a  given  circuit  is  800 
amperes,  and  the  resistance  of  that  circuit  is 
known  to  be  15  ohms.  What  is  the  horse  power 
expended  ? 

Ans.  —  In  this  case  C  =  800  and  R=15.  Sub- 
stituting these  values  in  Ohm's  law  the  equation 
becomes  /*7?*^' 

E 
800=  —  ,  or  E  =  15X  800  =  12,000. 

15 

That  is  to  say,  the  electromotive  force  on  that 
circuit  is  12,000  volts.  The  number  of  watts  = 
CxE  (amperes  multiplied  by  volts),  which  in  this 
case  is  800X12,000=9,600,000  watts.  Since  746 
watts  equal  one  horse  power, 
9,600,000 

—  =12,8684Jf  horse  power. 
746 

The  electromotive  force  of  a  given  current  is  500 


26  ELECTEIC    EAILWAY    MOTORS. 

/ 

volts,  and  the  resistance  of  the  circuit  is  25  ohms. 
How  many  horse  power  can  be  delivered  ? 

Ans. — E=500, 11=25.  Substituting  these  values, 
in  Ohm's  law  the  equation  becomes 
500 

C  = =20. 

25 

That  is  to  say,  the  current  that  will  flow  under 
these  conditions  will  be  20  amperes.  Watts= 
CxE  =  20X500  =  10,000  watts.  (This  may  also 
be  called  10  kilowatts.) 

watts     10,000 

Horse  power= = =  13f  Jf  horse  power. 

746         746 

Six  hundred  horse  power  are  delivered  over  a 
given  circuit,  the  electromotive  force  of  which 
is  500  volts.  What  is  the  current  ? 

Ans. — Since  1  horse  power  is  equal  to  746  watts, 
600  horse  power  will  be  equal  to  600X746  = 
447,600  watts. 

Since  watts  are  equal  to  the  volts  multiplied  by 
the  amperes,  there  will  be  as  many  amperes  as  500 
is  contained  times  in  447,600  watts  : 
447,600 

=  895£  amperes. 

500 

A  street  car  motor  is  generating  10  horse  power 
while  taking  35  amperes.  What  must  be  the 
electromotive  force  of  the  current  ? 

Ans.— 1  H.  P.  =  746  watts.  10  H.  P.  =  10X746 
watts =7460    watts.      Watts=CxE  =  7460.     But 
C  =  35.     Substituting  for  C  its  value, 
7460 

E= =  213-^  volts. 

35 


EXAMPLES.  27 

With  these  examples  the  use  of  Ohm's  law  anfl 
the  conversion  of  electrical  into  mechanical  units 
and  vice  versa  will  have  been  sufficiently  illus- 
trated to  show  the  extreme  simplicity  of  the 
operation.  It  would  be  well  for  those  desiring  to 
really  familiarize  themselves  with  electrical  prob- 
lems to  take  figures  which  they  may  obtain  from 
the  actual  operation  of  the  roads  with  which  they 
are  connected  and  attempt  their  solution  in  the 
same  manner.  By  watching  the  ammeter  and 
voltmeter  in  the  power  house  they  can  obtain  an 
endless  variety  of  problems  as  to  how  much  work 
is  being  done  on  the  line,  and  other  data  usually 
obtainable  at  the  office  will  enable  them  to  ring  in 
changes  on  these  problems  which  it  will  be  not 
only  interesting  but  exceedingly  instructive  to 
investigate. 


CHAPTER  IV. 

THE    ELECTRIC    CURRENT    AND    ITS    PROPERTIES. 

WHILE  all  fluids  resemble  each  other  in  some 
respects,  each  has  some  peculiarity  of  its  own  by 
which  it  is  distinguished  from  every  other  fluid, 
and  while  we  may  partially  describe  one  by  show- 
ing its  resemblances  to  other  liquids  or  fluids,  if 
we  go  no  further  than  this,  we  will  miss  the  very 
characteristics  by  which  this  particular  fluid 
^differs  from  the  others.  If  we  cannot  liken  these 
peculiarities  to  anything  else,  we  can  only  become 
familiar  with  them  by  experimenting  with  the 
liquid  itself  and  observing  the  peculiarities,  and 
perhaps  that  will  be  the  best  way  for  us  in  this 
case.  I  think  we  can  select  a  few  experiments 
which  will  cost  us  little  to  perform  and  require 
little  skill  to  prepare  which  will  not  only  familiarize 
us  with  many  of  the  peculiarities  of  the  electric 
current,  but  will  at  the  same  time  greatly  assist  us 
in  understanding  the  principle  upon  which  the 
electric  motor  operates,  and  it  is  proposed  in  this 
chapter  to  give  a  few  of  these,  with  full  instruc- 
tions how  to  prepare  and  perform  them. 

A  word  of  advice  here  is  that  two  or  three 
motormen  perform  these  experiments  together 
and  divide  the  expense  of  the  material.  This 
method  will  have  several  advantages,  one  of  which 
is  that  where  several  work  together  it  results  in 
mutual  benefit  through  discussions  of  the  "  whys  " 
and  "  wherefores  "  of  the  phenomena,  and  this,  it 

28 


THE    ELECTRIC    CURRENT.  29 

must  be  understood,  is  what  we  must  strive  after  in 
all  cases  ;  to  know  why  a  thing  is  so,  as  far  as  it  is 
possible  to  know  it,  and  in  those  cases  where  it  is 
impossible  to  know  why  a  thing  is  so  we  must 
endeavor  to  satisfy  our  minds  whether,  if  it  is  so, 
it  is  always  so  or  only  occasionally  or  accidental!}7 
so.  If  it  is  always  so,  and  we  are  satisfied  of  that 
fact,  it  is  then  a  law.  If  it  is  only  occasionally 
so,  then  there  is  surely  some  reason  why  it  is  ever 
so  or  why  it  is  not  always  so,  and  we  must  not  be 
satisfied  until  we  have  discovered  this  reason. 
That  is  the  scientific  way  of  doing  things,  and  in 
fact  the  only  satisfactory  way.  Another  advan- 
tage in  working  together  is  that  by  sharing  the 
expense  of  the  material  among  two  or  three  it 
need  not  exceed  an  amount  which  any  motorman 
can  spare.  If  there  be  three  together,  seventy- 
five  cents  apiece  should  buy  everything  that  is 
needed,  and  I  feel  sure  that  the  entertainment  and 
benefit  that  will  be  derived  from  this  investment 
will  many  fimes  repay  the  outlay. 

Thus  far  the  flow  of  an  electric  current  in  a 
wire  has  been  likened  to  the  flow  of  water  in  a 
pipe,  and  in  fact  the  resemblance  is  so  strong  that 
many  electrical  phenomena  may  be  clearly  pre- 
dicted if  we  assume  that  our  conductor  is  a  small 
pipe  and  the  electric  current  is  a  current  of  water 
flowing  through  that  pipe  urged  along  under  a 
given  pressure. 

Some  years  ago  the  writer  became  acquainted 
with  a  German  mechanic  who  was  at  that  time 
in  charge  of  the  shops  of  one  of  our  largest  elec- 
trical factories,  and  who  had  already  gotten 
out  a  number  of  inventions  on  minor  details  of 
electrical  apparatus  that  were  of  the  utmost 
benefit  to  the  concern  that  employed  him  and 


30  ELECTRIC    RAILWAY    MOTORS. 

which  are  in  use  to-day.  In  conversation  with 
this  mechanic  one  day  he  told  the  writer  that 
he  had  never  had  any  instruction  in  electricity 
whatever.  Upon  being  asked  how  it  was  pos- 
sible, then,  for  him  to  devise  such  excellent  elec- 
trical apparatus,  he  replied  that  he  had  been 
educated  as  a  hydraulic  engineer  and  understood 
the  mathematics  of  the  flow  of  water  through 
pipes  thoroughly,  and  that  when  he  wanted  to 
know  how  the  electric  current  would  act  under 
new  conditions  he  simply  assumed  that  he  was 
dealing  with  water,  figured  out  his  problem  ac- 
cordingly, and  was  pretty  sure  to  find  that  his 
results  with  electricity  would  correspond. 

But  while  the  flow  of  electricity  corresponds 
closely  in  many  respects  with  the  flow  of  water, 
it  differs  radically  from  it  in  many  others,  and  it 
is  some  of  these  differences  that  the  following  ex- 
periments are  intended  to  show. 

To  start  with,  we  must,  of  course,  have  a  gen- 
erator of  electricity,  and  for  this  purpose  any 
cheap  primary  battery  will  answer.  If  it  is  de- 
sired to  make  the  battery  one's  self,  it  can  be  done 
very  simply  and  cheaply  and  will  prove  both  in- 
teresting and  instructive.  The  galvanic  battery 
depends  upon  the  simple  principle  that  if  two 
unlike  substances  that  are  conductors  of  electric- 
ity are  immersed  at  one  end  in  a  liquid  capable  of 
acting  upon  or  corroding  one  of  them  more  than 
the  other,  and  the  other  ends  of  these  (the  two 
ends  not  immersed  in  the  liquid)  be  connected  to- 
gether by  a  wire,  a  current  of  electricity  will  at  once 
flow  through  that  wire.  Since  almost  all  chemicals 
corrode  metals  to  at  least  some  extent,  and  hardly 
ever  corrode  any  two  metals  to  exactly  the  same 
extent,  it  would  be  almost  impossible  to  select  any 


THE   ELECTEIC    CURRENT. 


31 


two  metals  or  any  two  conductors  of  electricity 
which  would  not  form  a  battery  if  immersed  in 
any  solution  we  choose  to  employ.  We  therefore 
have  an  almost  infinite 
variety  of  materials  z 
to  choose  from  with 
which  to  make  our 
battery,  but  of  course 
they  do  not  all  make 
equally  good  batteries. 
If  we  can  find  two  sub- 
stances, one  of  which 
is  very  rapidly  and 
easily  corroded  by  our 
solution  and  the  other 
not  corroded  at  all, 
then  we  have  the  ele- 
ments of  a  good  bat- 
tery. If  the  solution 
and  both  of  the  sub- 
-  stances  which  are  im- 
mersed in  it  are  cheap, 
so  much  the  better. 
Now  it  happens  that 
zinc  is  both  cheap  and 
readily  soluble  in  a 
large  number  of  solutions,  and  carbon  is  also  cheap 
and  practically  insoluble  in  all  solutions,  so  zinc 
and  carbon  are  usually  employed  in  all  modern 
batteries.  It  is  a  peculiar  fact  that  a  solution  of 
table  salt  in  water  will  not  corrode  zinc  when 
acting  upon  it  alone,  nor  will  it  corrode  the  zinc  if 
there  be  placed  in  the  same  vessel  with  it  a  stick 
of  carbon,  so  that  the  two  might  remain  together 
in  the  same  solution  almost  indefinitely,  if  they 
do  not  touch,  without  the  zinc  being  corroded  at 


FIG.  1. 


32  ELECTRIC    RAILWAY    MOTORS. 

all,  but  if  their  outer  ends  be  connected  by  a 
wire,  the  salt  water  will  at  once  begin  to  attack 
the  zinc,  and  an  electric  current  will  commence 
to  flow,  and  continue  until  either  the  zinc  is  used 
up  or  the  salt  water  has  dissolved  so  much  of  it 
that  it  cannot  dissolve  any  more — that  is,  provid- 
ing the  zinc  and  carbon  remain  connected  by  the 
wire,  but  the  corrosion  of  the  zinc  will  at  once 
cease  if  this  connection  be  broken.  This  property 
of  salt  water  and  zinc  renders  thempecularily  suita- 
ble substances  to  employ  in  electrical  batteries, 
because  if  the  carbon  and  zinc  be  disconnected 
when  the  battery  is  not  in  use,  there  is  no  waste 
of  material  and  the  battery  is  always  ready  for 
use,  requiring  only  that  the  zine  and  carbon  be 
connected  again  to  start  the  current  to  flowing. 

While  an  excellent  battery  may  be  made  with  a 
solution  of  ordinary  table  salt,  there  is  still  a  bet- 
ter substance  for  this  purpose,  sal  ammoniac,  which 
is  almost  equally  cheap  and  quite  as  harmless  to 
handle. 

To  make  a  battery,  procure  a  wide-mouthed  jar 
either  of  earthenware  or  glass,  and  buy  a  stick  of 
battery  carbon  about  two  inches  wide,  one-fourth 
inch  thick  and  eight  inches  long,  and  also  a  "  pen- 
cil zinc."  These  may  be  procured  of  any  electrical 
supply  dealer,  and  should  both  be  provided  at  their 
upper  ends  with  binding  posts  or  means  to  facili- 
tate the  attachment  of  wires.  The  carbon  will 
cost  ten  cents  and  the  zinc  five  cents.  At  the 
same  place  or  at  the  nearest  drug  store  five  cents' 
worth  of  sal  ammoniac  should  be  purchased,  and 
we  have  all  that  is  necessary  to  make  a  fairly 
good  electric  battery. 

Empty  the  sal  ammoniac  into  the  jar  and  fill  it 
three-quarters  full  of  water,  and  when  it  is  dis- 


THE    ELECTRIC    CURRENT.  33 

solved  insert  the  carbon  and  zinc  with  their  bind- 
ing posts  up.  If  we  had  an  electric  bell,  and  should 
connect  one  of  its  binding  posts  to  the  binding 
post  of  the  zinc  and  the  other  to  the  binding  post 
of  the  carbon,  the  bell  would  ring  vigorously  and 
continue  to  ring  for  a  long  time,  showing  that 
quite  a  strong  current  was  flowing.  If  we  had 
used  table  salt  instead  of  sal  ammoniac  the  only 
difference  would  have  been  that  the  battery  would 
not  last  so  long  and  the  current  would  not  be  quite 
so  strong. 

Fig.  1  shows  a  battery  such  as  described  above, 
the  zinc  pencil  being  marked  Z  and  the  carbon 
marked  C.  In  using  such  a  battery,  or  "  cell,"  as 
it  is  more  properly  called,  it  is  better  not  to  let  the 
zinc  and  carbon  touch  each  other  in  the  liquid,  and 
they  must  not  be  allowed  to  touch  each  other  out- 
side the  liquid,  for  if  they  do  it  is  the  same  as 
though  they  were  connected  by  a  wire,  and  if 
allowed  to  remain  this  way  when  not  in  use  the 
battery  will  soon  become  entirely  exhausted.  For 
the  reason  that  a  little  jarring  might  cause  the  zinc 
and  carbon  to  come  in  contact  with  each  other 
when  the  cell  is  not  in  use,  it  would  be  a  wise  pre- 
caution to  remove  either  one  or  both  from  the 
liquid  before  setting  the  jar  away. 

It  may  perhaps  be  found  more  convenient  to 
buy  a  battery,  and  if  so  a  good  dry  battery,  which 
can  be  bought  for  fifty  cents,  will  be  found  as  con- 
venient as  any.  With  the  dry  battery  there  is  no 
danger  of  spilling  any  liquid,  and  the  zinc  and  car- 
bon are  fastened  in  so  that  there  is  no  possibility 
of  their  coming  in  contact  with  each  other. 

In  a  galvanic  cell  such  as  either  of  the  above, 
the  current  is  supposed  to  flow  through  the  wire 
from  the  least  soluble  element  to  the  one  most 


34  ELECTRIC    RAILWAY    MOTORS. 

readily  corroded  by  the  battery  fluid.  Where  the 
elements  are  carbon  and  zinc  as  above,  the  current 
must  always  be  considered  as  flowing  from  the 
carbon  through  the  wire  to  the  zinc.  The  carbon 
is  therefore  called  the  positive  pole,  and  the  zinc 
the  negative  pole,  and  correspond  respectively  to 
the  positive  brush  of  the  dynamo,  from  which  the 
current  is  supposed  to  flow,  and  the  negative 
brush,  through  which  it  returns  to  the  dynamo. 

In  addition  to  procuring  the  foregoing,  an  eight- 
ounce  spool  of  No.  24  cotton-insulated  copper  wire 
should  be  purchased  to  complete  the  equipment 
for  the  following  experiments.  This  can  be  had 
wherever  the  other  supplies  are  purchased  for  forty 
cents. 

In  preparation  for  the  experiments,  cut  out  a 
piece  of  brown  manilla  or  ordinary  writing  paper 
about  two  inches  square,  and  wrap  this  carefully 
into  a  cylinder  around  an  ordinary  lead  pencil.  A 
round  lead  pencil  is  better  for  this  purpose  than 
an  octagonal  pencil.  Next  take  the  spool  of  in- 
sulated wire,  and  while  the  paper  is  still  on  the  lead 
pencil,  beginning  at  the  left-hand  end  of  the  paper, 
overwind  it  tightly  and  closely  with  the  wire  until 
the  right-hand  end  of  the  paper  is  reached.  Then 
overwind  this  laydr  again  with  another  layer,  pro- 
ceeding to  the  left,  and  then  with  a  second  layer 
winding  to  the  right,  and  to  prevent  the  wire  from 
becoming  loose  at  either  end  wind  them  with  a 
few  turns  of  strong  thread  or  string  and  tie  tightly. 
The  wire  may  now  be  cut  from  the  spool,  leaving 
an  end  beyond  the  coil  of  three  or  four  inches. 
There  should  be  about  the  same  length  of  loose 
wire  left  at  the  beginning  of  the  coil.  The  paper 
cylinder  with  its  overwrapped  coils  may  now  be 
slipped  from  the  pencil  and  we  have  a  hollow 


THE  ELECTRIC  CURRENT.  35 

cylinder  of  paper  overwound  with  three  layers  of 

insulated  wire,  the  two  ends  of  which,  each  some 

three  or  four  inches  long,  extend  out  loosely,  as  in 

Fig.  2.     The  in- 

sulation     should  > 

be   carefully   re- 

moved    with     a 

knife  from  about        ______  _ 

an  inch  of  both  j^   g 

ends  of  the  wire 

to  enable  the  coil  to  be   placed   in  the   circuit   of 

the  battery. 

Cut  off  "from  the  spool  two  more  pieces  of  wire 
each  about  a  foot  long,  and  after  removing  the 
insulation  from  both  ends  of  these  for  an  inch  or 
two,  fasten  one  end  of  one  in  the  zinc  binding  post 
and  one  end  of  the  other  in  the  carbon  binding 
post.  To  the  loose  ends  of  the  two  wires  twist 
the  two  loose  ends  of  the  small  coil  just  made.  If 
this  is  properly  done,  the  carbon  and  zinc  will  be 
connected  by  wire,  and  the  current  will  flow  from 
the  carbon  around  the  various  windings  of  the  coil 
to  the  zinc.  But  as  yet  we  have  no  evidence  of 
this  fact.  Procure  a  large  darning  needle  and 
insert  it  point  first  into  the  hollow  coil,  and  after 
allowing  it  to  remain  there  a  few  minutes  take  the 
needle  out  and  examine  it.  No  change  will  be 
observed  —  it  is  apparently  exactly  like  the  needle 
that  was  put  in  there  a  moment  before,  and  yet  one 
of  the  most  remarkable  changes  known  to  science 
has  quietly  taken  place.  Cut  a  small  piece  of  cork 
(about  the  size  of  a  good-sized  pea)  large  enough 
to  float  the  needle  in  water,  run  the  needle  through 
this  until  the  cork  is  in  the  middle  and  drop  the 
needle  with  its  float  into  a  saucer  full  of  water. 

The  needle  will  swing  around  untiUt-points  exactly 

'^ 


OF  THE 

UNIVERSITY 


36  ELECTRIC    RAILWAY    MOTORS. 

north  and  south.  Reverse  the  position  of  the 
needle,  or  point  it  in  any  direction  we  choose,  it 
will  swing  around  so  that  it  points  north  and  south 


FIG.  3. 

again.  If  on  first  trying,  the  point  of  the  needle 
turns  toward  the  north  and  the  eye  toward  the 
south,  it  will  always  take  up  the  same  position  again, 
the  point  always  turning  toward  the  north  and  the 
eye  toward  the  south.  The  act  of  passing  the  cur- 
rent around  the  needle  while  inside  the  coil  has 
given  ib  this  remarkable  property,  that  ever  after- 
ward when  free  to  move  it  will  take  up  a  north  and 
south  position,  and  the  same  end  will  always  point 


THE     ELECTRIC   CURRENT. 


37 


north.  "We  have  magnetized  the  needle,  and  by 
rendering  it  free  to  move  whichever  way  it  likes 
have  made  one  of  the  most  remarkable  instruments 
the  world  has  ever  seen,  viz.,  a  compass. 

Place  another  needle  in  the  coil  in  the  same 
way — point  first — and  then  float  it  on  water.  If 
the  first  needle  took  up  a  position  with  its  point 


FIG.  4. 


toward  the  north  the  second  one  will  do  the  same, 
and  when  it  has  come  to  rest  its  point  will  be 
toward  the  north  and  its  eye  toward  the  south. 

Try  a  third  needle,  but  introduce  this  into  the 
coil  eye  first.  Float  this  and  the  eye  will  be 
toward  the  north  instead  of  the  point.  We  have 
discovered  two  laws,  one,  that  a  needle  which  has 
been  placed  in  a  coil  through  which  an  electric 
current  is  passing  acquires  the  property  of  taking 
up  a  north  and  south  position  when  free  to  move, 
the  same  end  always  turning  toward  the  north; 
and  second,  that  every  needle  which  is  placed  in 
that  coil  in  the  same  way  will  act  in  the  same  way, 
and  the  end  which  goes  in  first  will  always  be  the 
one  to  point  north  if  that  was  the  one  that  pointed 
north  in  the  first  experiment.  For  these  reasons 
the  north  end  of  the  needle  is  called  the  north-seek- 
ing pole  and  the  other  the  south-seeking  pole. 


38  ELECTRIC   RAILWAY   MOTORS. 

While  one  of  the  needles  is  floating  in  the  water, 
if  we  bring  the  north-seeking  pole  of  another 
needle  near  its  north  pole,  it  will  rapidly  repel  it. 
If,  on  the  contrary,  we  bring  a  north  pole  near  a 
south  pole,  the  two  will  attract  each  other  strongly, 
and  the  floating  needle  will  rush  to  and  attach 
itself  to  the  other  so  strongly  that  it  may  with 
care  be  lifted  out  of  the  water.  In  fact,  we  have 
two  magnets  with  which  we  can  produce  all  the 
phenomena  of  magnetism  with  which  everyone  is 
familiar. 

Now  let  us  remove  our  coil  from  the  battery 
circuit  and  insert  in  its  stead  a  straight  piece  of 
wire,  say  a  foot  long,  by  twisting  its  two  ends  to 
the  battery  wires,  and  then  stretch  it  in  a  north 
and  south  direction  directly  over  our  floating 
needle  or  compass.  It  will  be  observed  that  the 
latter  is  deflected  through  a  considerable  angle 
from  its  former  north  and  south  position,  and  if  the 
wire  be  over  the  needle  the  deflection  will  always 
be  in  the  same  direction.  If  we  examine  closefy, 
we  will  find  that  if  the  current  is  flowing  from 
north  to  south  the  needle  will  always  be  deflected 
to  the  east.  If  we  reverse  our  wire,  however,  so 
that  the  current  is  flowing  from  south  to  north,  the 
deflection  will  be  to  the  west.  Place  the  wire 
under  the  saucer,  or  even  under  the  table  upon 
which  the  saucer  rests,  and  if  the  distance  be  not 
too  great  the  needle  will  be  again  deflected,  but  in 
the  opposite  direction,  viz.,  if  the  current  flows 
through  the  wire  from  north  to  south  under  the 
needle,  its  north  pole  will  be  deflected  to  the  west, 
and  if  the  wire  be  reversed  so  that  the  current 
flows  from  south  to  north,  the  north  end  of  the 
needle  will  be  deflected  to  the  east. 


CHAPTER  V. 

THE    ELECTRIC    CURRENT   AND   ITS   PROPERTIES. 

T  (Continued.) 

WE  have  now  discovered  one  radical  difference 
between  the  flow  of  water  in  pipes  and  the  flow  of 
an  electric  current  in  a  conductor.  In  the  case  of 
water  its  flow  within  a  pipe  produces  absolutely 
no  external  effect,  but  in  the  case  of  electricity  we 
find  that  its  flow  produces  quite  a  marked  influence 
within  the  space  surrounding  the  wire.  In  the 
case  of  the  coil  by  which  we  magnetized  the  nee- 
dles none  of  the  current  could  possibly  have  gotten 
to  the  needles,  first,  because  the  wire  of  which  the 
coil  was  composed  was  carefully  insulated  with 
cotton  thread,  which  effectually  prevented  the 
escape  of  current  from  the  wire,  and  second,  there 
were  several  thicknesses  of  paper  between  the 
needle  and  the  coil,  and  dry  paper  is  one  of  the 
best  electrical  insulators  known.  We  might  have 
inclosed  our  needles  in  India  rubber  or  glass  before 
inserting  them  in  the  coil  as  a  further  protection 
against  the  current,  but  the  result  would  have  been 
the  same  exactly.  We  have  also  shown  that  if  a 
wire  in  which  a  current  is  passing  is  held  either 
above  or.  below  a  compass  needle  the  influence  of 
the  current  upon  the  needle  is  manifested  by  a 
deflection  either  to  the  west  or  east  of  its  normal 
north  and  south  direction,  and  further,  that  we  can 
not  only  thus  tell  whether  a  current  is  flowing  in  a 


40  ELECTRIC    RAILWAY    MOTORS. 

wire  or  not,  but  we  can  tell  in  which  direction  it  is 
flowing. 

We  have  seen  that  if  a  current  flows  from  north 
to  south  over  the  needle  it  deflects  it  to  the  east, 
and  that  it  also  deflects  it  to  the  east  if  it  flows 
from  south  to  north  under  the  needle.  If,  there- 
fore, we  form  a  loop  of  our  wire,  in  the  center  of 
which  we  place  our  saucer  of  water  and  needle  so 

that  the  current  flows 
first  from  north  to 
south  over  and  then 
from  south  to  north 
under  the  needle  (Fig. 

\i      5.),  the   effect  of   the 
)     one    current     is     just 
doubled.    If  two  loops 
are  made,  so  that  the 
current     passes     over 
FIG.  5.  the  needle  twice  from 

north    to    south    and 

twice  under  the  needle  from  south  to  north,  the 
effect  of  the  current  will  be  multiplied  four 
times.  By  increasing  the  number  of  loops  in  this 
way  we  are  enabled  to  produce  quite  percepti- 
ble deviations  with  such  feeble  currents  that  they 
could  scarcely  be  detected  in  any  other  way.  We 
hav.e,  in  fact,  actually  made  a  galvanometer.  As 
winding  the  wire  above  the  needle  in  many  turns 
would  hide  the  needle  so  that  we  could  not  see  its 
deflections,  it  is  more  usual  in  making  galvanom- 
eters to  wind  the  wire  in  a  flat  coil  and  place  it 
under  the  needle.  While  the  multiplying  effect 
of  a  coil  thus  arranged  is  not  as  great  as  in  the 
arrangement  described,  the  instrument  itself  is 
much  more  convenient  to  use.  To  make  such  a 
coil  cut  out  a  piece  of  cigar  box,  or  other  lumber  of 


THE    ELECTEIC    CURRENT. 


41 


about  that  thickness,  about  2  inches  wide  and 
2J-  long  (Fig.  6).  Cut  away  a  seat  on  both 
ends  for  the  wire  and  at  opposite  corners  of  one 
end  bore  a  small  hole  about  the  diameter  of  a 


PIG.  6. 

pin  to  hold  the  ends  of  the  wire.  Into  one  of 
these  insert  the  end  of  the  wire  from  the  spool  and 
pull  it  through  about  five  or  six  inches  and  plug  up 
the  hole  with  a  piece  of  wood  so  as  to  hold  the 
wire  tightly  in  place.  Then  wind  on  tightly  eighty 
to  a  hundred  turns  of  the  wire  and  end  it  off 
through  the  other  hole,  plugging  it  up  and  leaving 
an  end  of  about  five  or  six  inches  as  before.  Now 
place  the  coil  under  the  saucer  and  its  floating 
needle  and  you  have  a  very  delicate  galvanom- 
eter by  which  currents  that  would  otherwise 
scarcely  be  suspected  can  be  detected.  Connect 
the  two  ends  of  the  coil  with  the  battery  wires 
and  the  deviation  of  the  needle  will  be  found  to  be 
much  greater  and  more  rapid  than  in  the  previous 
experiments. 


42  ELECTRIC    RAILWAY    MOTORS. 

It  must  be  borne  in  mind  that  the  tendency  of 
a  current  passing  either  above  or  below  a  compass 
needle  is  to  place  that  needle  at  right  angles  to  the 
direction  of  the  current.  The  strongest  current 
will  therefore  only  cause  the  needle  to  take  up 
a  position  at  right  angles  to  it — it  will  never  cause 
it  to  deviate  further  or  to  reverse  itself. 

THE    SOLENOID. 

Now  let  us  return  to  our  first  coil  of  wire  (Fig.  2, 
see  page  35).  A  hollow  coil  of  wire  such  as  this  is 
called  a  solenoid,  and  it  has  some  very  peculiar 
properties  which  it  will  be  necessary  for  us  to 
understand  before  we  can  thoroughly  comprehend 
either  the  dynamo  or  motor,  and  as  we  now  have 
all  the  apparatus  necessary  to  investigate  these 
properties  we  will  begin  at  once. 

Take  one  of  our  magnetized  needles  and  sus- 
pend it  at  its  middle  point  by  a  very  fine  thread, 
so  that  the  needle  will  hang  horizontally  and  be 
free  to  move.  Now  connect  up  the  solenoid  with 
the  battery  and  present  first  one  end  of  the  sole- 
noid and  then  the  other  to,  say,  the  north  pole  of 
the  needle.  It  will  be  found  that  one  end  attracts 
and  the  other  repels  this  pole  just  as  would  a  real 
magnet,  and  that  the  end  that  repels  the  north 
pole  attracts  the  south  pole.  In  fact,  although 
there  is  no  iron  or  other  magnetic  material  in  the 
solenoid,  it  acts  exactly  like  a  magnet,  and  is  one 
so  long  as  the  current  flows  through  it.  If  the 
pole  of  the  needle  which  the  solenoid  attracts  be 
properly  directed,  the  solenoid  will  suck  the 
needle  almost  entirely  within  itself,  and  if  the 
needle  be  reversed  and  pushed  inside  of  the  coil,  it 
will  be  expelled  again  as  soon  as  the  fingers  are 
removed  from  it  so  as  to  permit  of  it.  Thus  it 


THE    SOLENOID.  43 

will  be  seen  that  a  solenoid  has  a  north  and  south 
pole,  just  as  has  a  steel  magnet,  so  long  as  a  cur- 
rent is  passing  through  it.  Now  detach  one  of  the 
battery  wires  from  its  binding  post,  so  that  the 
current  can  no  longer  pass  through  the  solenoid, 
and  repeat  these  experiments.  It  will  be  found 
to  be  entirely  inert,  and  will  neither  attract  nor 
repel  either  pole  of  the  needle.  The  magnetic 
property  of  the  solenoid  is  therefore  evidently 
entirely  due  to  the  current  which  is  passing 
through  it. 

The  phenomenon  of  sucking  in  or  expelling  a 
magnetized  needle  may  be  better  illustrated,  per- 
haps, by  partly  inserting  the  needle  in  the  solenoid 
while  one  of  the  battery  wires  is  disconnected,  and 
then  suddenly  closing  the  circuit  by  touching  the 
binding  post  with  the  disconnected  wire.  Thus 
far  we  have  been  experimenting  with  a  highly 
tempered  hard  steel  needle.  We  have  found  that 
when  it  is  once  magnetized  it  remains  a  magnet 
permanently.  Now  let  us  repeat  our  experiments, 
using  a  short  piece  (two  or  three  inches  long)  of 
soft  iron  wire.  Before  we  attempt  to  magnetize 
it  let  us  try  it  with  our  compass  needle.  We  find 
that  it  attracts  both  ends  equally  well.  There 
is  under  no  conditions  any  repulsion,  because  it  is 
not  magnetized.  Place  it  in  the  solenoid  as  we 
did  when  magnetizing  the  needle,  and  while  still 
in  the  solenoid  test  it  with  the  compass.  We 
find  that  one  end  attracts  and  the  other  repels 
either  end  of  the  compass  needle  just  as  did  our 
permanently  magnetized  needle  before,  and  even 
more  strongly.  Remove  the  wire  from  the  sole- 
noid and  try  it  again.  We  find  it  repels  neither 
end,  but  attracts  both,  as  it  did  before  it  was  mag- 
netized. Suspend  the  wire  in  the  middle  and 


44  ELECTEIC   EAILWAY   MOTORS. 

approach  the  solenoid  to  it.  The  latter  will  attract 
both  ends  equally  well  and  suck  in  either  end 
with  equal  facility.  The  soft  iron  wire  is  no 
longer  a  magnet.  It  was  a  stronger  magnet  while 
in  the  solenoid  than  the  needle^  was,  but  imme- 
diately it  is  taken  out  or  the  current  in  the  sole- 
noid is  broken  it  loses  its  magnetism.  This  may 
be  more  clearly  illustrated  by  causing  the  wire, 
while  in  the  solenoid,  to  pick  up  another  small 
piece  of  the  same  wire,  and  then  detaching  one  of 
the  battery  wires  from  its  binding  post.  Imme- 
diately the  current  is  broken  the  wire  will  drop 
its  load,  and  it  will  remain  incapable  of  picking 
it  up  again  until  the  current  is  started  in  the 
solenoid. 

There  is,  therefore,  this  very  great  difference 
between  hard  tempered  steel  and  soft  annealed 
iron,  that  the  former  when  once  magnetized  retains 
its  magnetism  permanently,  while  the  latter  loses 
it  immediately  the  encircling  current  is  stopped. 

There  are  also  other  minor  differences,  among 
which  may  be  mentioned  the  following  :  Tem- 
pered steel  requires  an  appreciable  time  to  mag- 
netize, whereas  soft  iron  seems  to  assume  the 
property  instantaneously.  It  is  somewhat  difficult 
to  change  the  direction  of  magnetism  of  steel — 
that  is,  after  having  magnetized  a  steel  bar,  so  that 
one  end  is  north  and  the  other  south,  to  demag- 
netize it  and  magnetize  it  again,  so  that  the  ends 
which  were  formerly  north  and  south  will  become 
respectively  south  and  north — while  with  soft  iron 
the  change  is  made  with  the  greatest  facility.  A 
given  current  flowing  through  a  solenoid  of  a 
given  number  of  turns  will  make  a  much  stronger 
magnet  out  of  a  soft  iron  bar  than  it  will  out  of  a 
steel  bar  of  the  same  dimensions. 


THE    SOLENOID.  45 

Within  certain  limits  the  amount  of  magnetism 
that  can  be  imparted  to  a  bar  of  iron  or  steel  in- 
creases with  the  number  of  amperes  of  current 
passing  through  the  solenoid  and  the  number  of 
turns  in  the  coil.  A  limit  is  finally  reached,  how- 
ever, beyond  which  neither  an  increase  of  current 
nor  an  increase  in  the  number  of  turns  or  windings 
in  the  solenoid  will  materially  increase  the  mag- 
netism. With  tempered  steel  this  limit  is  much 
sooner  reached  than  with  soft  annealed  iron.  For 
this  reason,  of  two  magnets  of  iron  and  steel  of 
exactly  the  same  size  the  one  of  soft  iron  can  be 
made  by  far  stronger  than  it  is  possible  to  make 
the  one  of  steel.  Cast  iron,  which  partakes  more 
of  the  nature  of  steel  than  of  soft  or  wrought  iron, 
is  also  inferior  to  the  latter  for  magnetic  purposes 
and  loses  its  magnetism  less  readily.  In  fact,  the 
best  wrought  iron  that  has  been  rolled  or  drawn, 
and  not  subsequently  softened  again  by  annealing 
processes,  possesses  the  property  of  retaining  some 
of  its  magnetism  for  quite  a  while  and  is  less  suit- 
able for  magnetic  purposes,  especially  where  it  is 
desired  to  have  the  magnetism  undergo  rapid 
changes  either  of  direction  or  intensity.  All  of 
these  points  have  an  important  bearing  upon  motor 
and  dynamo  construction,  and  will  be  referred  to 
again  later  on. 

Another  point  which  has  also  a  bearing  upon  a 
subject  to  be  taken  up  in  a  subsequent  chapter 
may  be  referred  to  here. 

As  everyone  knows,  a  knife  or  a  piece  of  steel 
may  be  magnetized  by  rubbing  it  against  another 
magnet.  It  may  also  be  more  slowly  magnetized 
by  laying  the  two  side  by  side  for  some  time  even 
without  touching  each  other.  Now  the  earth  itself 
is  a  huge  magnet  with  a  north  and  a  south  pole 


46  ELECTEIC    RAILWAY    MOTORS. 

just  like  the  small  magnets  we  have  made,  and  it 
is  the  attraction  of  the  earth's  north  pole  for  the 
compass  needle  that  causes  the  latter  to  point 
always  to  the  north.  Since  two  north  or  two  south 
poles  never  attract  each  other,  but  repel,  the  end 
of  the  needle  that  points  to  the  earth's  north  pole 
is  really  a  south  pole,  and  should  not  be  called  a 
north  pole  at  all ;  this  is  the  reason  that  when  it 
was  first  referred  to  in  this  book,  particular  care 
was  taken  to  call  it  the  "  north-seeking  pole."  It 
is,  however,  usually  called  the  north  pole,  because 
it  points  toward  the  north,  and  will  hereafter  be 
referred  to  by  this  name. 

But  to  return  to  our  subject.  If  the  earth  is 
really  a  magnet,  we  would  expect  bars  of  iron  lying 
approximately  parallel  with  the  line  joining  its  two 
poles  to  become  in  time  magnetized,  and  as  a  mat- 
ter  of  fact  they  do.  Bars  standing  in  a  vertical 
position  seem  to  become  magnetized  more  rapidly, 
perhaps,  than  those  lying  horizontal^,  but  those 
^^j^^'  lying  in  a  north  and  south  direction,  in  clinging 
'downward  toward  the  earth  at  such  an  angle  as 
to  point  directly  toward  the  north  pole,  become 
magnetized  still  more  quickly,  and  the  magnetiza- 
tion is  rendered  almost  instantaneous  if  the  bar 
while  held  at  this  angle  is  smartly  struck  on  either 
end  with  a  hammer. 

This  experiment  may  be  easily  tried  with  an 
ordinary  poker.  After  hitting  it  a  tap  on  the  end 
bring  the  end  which  was  pointed  toward  the  earth 
near  the  compass  needle.  It  will  smartly  repel 
the  north  pole  and  attract  the  south  pole.  Reverse 
the  poker  and  hit  it  another  tap  and  test  it  with 
the  compass  ;  the  polarity  will  be  found  to  have 
been  reversed.  The  end  which  at  first  repelled 
the  north  pole  will  now  attract  it  and  repel  the 


THE    SOLENOIP.  47 

south  pole.  Now  there  is  a  curious  thing  that  we 
can  do.  We  have  literally  knocked  magnetism 
into  the  poker  in  the  first  place,  and  we  have  by 
reversing  the  poker  and  striking  it  again  knocked 
a  north  pole  out  of  one  end  into  the  other,  and 
now  we  can  knock  the  magnetism  entirely  out  of 
the  poker  if  we  know  how  to  do  it.  Hold  the 
poker,  which  we  will  say  is  already  magnetized, 
horizontally  in  an  east  and  west  direction  and  hit 
it  one  or  two  smart  raps  on  either  end.  Now  test 
it  with  the  needle  and  it  will  be  found  to  attract 
either  end  equally  well,  thus  proving  that  the 
magnetism  has  entirely  disappeared. 


CHAPTER  VI. 

MEASURING   THE    CURRENT. 

BEFORE  passing  on  to  another  subject  it  may  be 
well  to  call  attention  to  something  else  we  have 
accomplished  in  the  simple  instruments  we  have 
made.  We  have  talked  of  amperes  and  volts  and 
ohms,  the  three  yardsticks  by  which  we  measure 
electrical  phenomena,  and  have  solved  a  number 
of  problems  involving  these  terms,  but  have  said 
nothing,  as  yet,  as  to  how  the  volts  and  amperes 
of  a  current'  or  the  ohms  of  a  circuit  are  deter- 
mined. We  are  all  probably  aware  that  the 
amperes  are  measured  by  an  ammeter  and  the 
volts  by  a  voltmeter,  but  we  may  not  know  on 
what  principle  either  of  these  instruments  is  con- 
structed. We  do  know,  however,  that  if  we  have 
the  volts  and  amperes  we  can  determine  the  re- 
sistance in  ohms  by  Ohm's  law,  but,  as  a  matter 
of  fact,  we  have  constructed  a  device  which,  by 
slight  modification,  is  capable  of  measuring  both 
the  volts  and  amperes. 

We  have  already  stated  incidentally  that  the 

magnetizing  power  of  a  solenoid  is  equal  to  the 

/number  of  amperes  flowing  through  it  multiplied 

N^y  the  number  of  convolutions  or  windings.     To 

state  it  in  another  way,  the  amount  of  pull  which 

a  solenoid  will  exert  upon  a  soft  iron  core  partly 

inserted  is  also  proportional  to  the  product  of  the 


MEASURING   THE    CURRENT. 

current  in  amperes  multiplied  by  the  number  of 
turns.  It  may  be  well  to  prove  this  roughly, 
which  we  can  do  by  suspending  again  our  short 
piece  of  soft  iron  wire  by  a  thread  tied  to  its 
center  and  proceeding  as  follows  :  Connect  up 


FIG.  7. 


the  battery  with  a  few  feet  of  wire  and  bend  its 
center  into  a  loop  of  one  turn  (Fig.  V)  and  present 
this  loop  to  one  end  of  the  wire.  We  have  here  a 
solenoid  of  one  turn,  and  it  will  tend  to  suck  the 
wire  into  itself.  The  attraction  will  be  compara- 
tively feeble,  to  be  sure,  but  much  stronger  than 
one  would  suppose  who  had  not  tried  it ;  but  note 
as  carefully  as  possible  its  strength.  Next  bend 
another  loop  so  that  we  have  a  solenoid  of  two 


50 


ELECTBIC    EAILWAY   MOTORS. 


turns  (Fig.  8).  The  pull  will  be  perceptibly 
stronger.  A  third  loop  will  increase  the  suction 
still  more,  and  so  on.  If  it  were  convenient  for  us 
to  do  it,  we  could  show  that  if  we  could  double  the 


FIG.  8. 


current  in  the  single  loop  the  increase  of  pull  would 
be  exactly  the  same  as  that  obtained  by  adding  a 
second  loop.  Now  if  we  have  a  solenoid  of  any 
number  of  turns — it  does  not  make  any  difference 
how  many — and  pass  a  known  current  through  it, 
and  measure  the  pull  on  the  dial  of  a  spring 
balance,  or  in  any  other  convenient  way,  marking 
the  point  where  the  dial  hand  rests  when  the  cur- 
rent is  on  full,  and  then  measure  the  pull  when 


MEASURING  THE  CURRENT.          51 

twice  this  current  and  three  times  and  four  times 
this  current  are  passing,  marking  each  time  the 
point  where  the  dial  hand  rests,  we  will  have  a 
meter  which  will  measure  the  current  passing  in 
terms  of  the  unit  used.  If  the  first  current  used 
was  one  of  one  ampere  and  the  second  one  of  two 
amperes,  etc.,  we  will  have  an  amperemeter  or 
ammeter.  Many  of  the  ammeters  used  in  street 
railway  power  stations  are  constructed  after  this 
plan,  only  the  solenoid  is  made  to  lift  a  weight 
instead  of  pulling  against  a  spring.  Since  the 
ammeter  is  intended  to  measure  the  full  current, 
it  is  always  placed  in  the  circuit,  so  that  all  of  the 
current  passes  through  its  coils  just  as  we  have 
placed  it  in  our  experiments  thus  far. 

A  voltmeter  may  be  regarded  as  a  more  delicate 
instrument  of  the  same  kind,  intended,  however, 
to  measure  only  a  very  small  portion  of  the  cur- 
rent. For  this  reason  it  is  made  of  very  high 
resistance,  for,  we  know  from  Ohm's  law,  that  of 
two  circuits  having  the  same  electromotive  force 
or  voltage  that  will  have  the  least  current  which 
has  the  highest  resistance.  Resistance  alone  would 
not  be  sufficient,  however,  for  with  the  exceedingly 
small  current  used  there  would  not  be  sufficient 
pull  to  operate  the  dial  hand  if  the  coil  were  made 
up  of  but  few  turns  of  a  high  resistance  wire  such 
as  German  silver.  The  coil  is  therefore  made  up 
of  the  best  conducting  copper  wire,  and  the  resist- 
ance is  obtained  by  making  this  wire  very  long 
and  bending  it  into  a  large  number  of  loops  or 
turns. 

In  operating  an  electric  motor  the  latter  does 
not  consume  amperes  any  more  than  a  water 
wheel  consumes  or  eats  up  gallons  of  water,  but 
it  does  consume  volts  just  as  the  water  wheel  con- 


52  ELECTRIC    RAILWAY    MOTORS. 

sumes  pounds  of  pressure.  In  the  water  wheel 
the  water  arrives  at  the  wheel  under  a  certain 
number  of  pounds  pressure,  and  after  it  has  gone 
through  the  wheel  and  done  its  work  it  flows 
away  under  a  lessened  pressure.  The  amount  of 
pressure  consumed  by  the  wheel  in  doing  its  work 
will  evidently  be  the  difference  of  pressure  at 
which  the  water  arrives  at  the  wheel  and  that 
under  which  it  flows  away.  So  with  the  electric 
motor  if  we  wish  to  know  the  amount  of  electro- 
motive force  (volts)  consumed  in  its  operation,  we 
measure  the  difference  of  potential  at  which  the, 


Line  Wire 


current  arrives  at  and  leaves  the  motor.  The  volt- 
meter is  used  to  make  this  measurement,  and  is 
placed  in  a  derived  or  shunt  circuit,  one  end  of 
which  is  connected  with  the  main  circuit  at  the 
positive  side  of  the  motor,  and  the  other  is  con- 
nected with  the  same  circuit  at  the  negative  side 
of  the  circuit,  and  the  amount  of  current  which 
will  flow  through  the  voltmeter  and  its  circuit  will 
be  proportional  to  the  difference  of  the  potentials 
between  the  positive  and  negative  sides  of  the 
motor.  In  Fig.  9  the  method  of  placing  the  volt- 
meter and  ammeter  in  circuit  is  shown. 


MEASURING  THE  CURRENT.          53 

From  this  it  will  be  seen  that  all  of  the  current 
which  goes  out  to  the  car  line  passes  through  a  few 
turns  of  the  coil  A,  which,  with  its  plunger  and 
weighted  lever,  index  hand  and  graduated  dial, 
constitutes  the  ammeter,  while  a  very  small  por- 
tion of  the  current  is  diverted  from  the  outgoing 
wire  to  the  return  wire  or  the  earth  through 
the  fine  wire  and  coil  of  many  convolutions,  By 
which,  with  its  plunger,  weighted  lever,  index 
hand  and  graduated  dial,  constitutes  the  voltmeter. 

Of  course  there  are  many  other  kinds  of  volt- 
meters and  ammeters  constructed  on  nearly  as 
many  different  principles,  but  we  have  not  space 
nor  is  it  worth  while  to  describe  them  here.  There 
is  such  an  instrument  as  an  ohmrneter,  which 
reads  directly  the  resistance  of  a  circuit,  but  it  is 
never  used,  so  far  as  the  writer  knows,  in  street 
railway  or  electric  lighting  equipments.  Resist- 
ances are  more  often  measured  by  means  of  an 
instrument  known  as  the  Wheatstone  bridge,  by 
which  the  unknown  resistances  are  compared 
with  coils  of  known  resistances,  enough  of  the  latter 
being  added  to  just  balance  the  unknown  resist- 
ance, exactly  as  we  weigh  an  unknown  quantity 
of  sugar  or  butter  by  placing  the  latter  in  one  pan 
of  our  scales  and  adding  pound  and  ounce  weights 
to  the  other  until  the  scales  are  exactly  balanced. 
But  as  the  motorman  is  not  likely,  as  such,  to  ever 
have  the  handling  of  a  bridge  or  be  required  to 
determine  very  accurately  the  resistances  either  of 
his  circuits  or  his  apparatus,  and  as  it  would  only 
needlessly  complicate  matters  at  this  time,  its 
description  will  be  omitted.  But  we  already  have 
the  means  of  determining  resistances  with  con- 
siderable accuracy  in  our  voltmeter  and  ammeter, 
as  before  stated,  for  if  we  introduce  these  two 


54  ELECTRIC   RAILWAY    MOTORS. 

instruments  properly  into  our  circuits  and  take 
their  readings  we  learn  the  number  of  amperes 
flowing  and  the  pressure  or  voltage  under  which 
that  flow  takes  place,  and  by  substituting  these 
values  in  Ohm's  law, 

E 
^\ 

~R 

the  resistances  are  readily  calculated. 

MAGNETISM    AND    ELECTROMAGNETISM. 

In  discussing  the  electric  current  we  likened  it 
to  a  flow  of  water  or  other  fluid  through  pipe, 
and  showed  that  this  flow  is  retarded  in  both  cases 
by  obstructions,  and  that  in  both  cases  these  obstruc- 
tions produced  like  results,  which  might  be  pre- 
dicted by  the  simple  relation  between  the  flow, 
pressure  and  resistance  expressed  in  Ohm's  law. 
We  further  found  that  in  the  case  of  electric  cur- 
rent the  influence  of  the  flow  within  the  wire 
extended  to  the  space  surrounding  the  wire,  and 
that  the  effect  of  this  influence  was  to  produce 
magnetism  in  that  space,  or,  as  electricians  would 
say,  to  produce  a  magnetic  field.  Thus  every  con- 
ductor carrying  a  current  of  electricity  produces 
in  the  space  surrounding  it  a  magnetic  field. 
That  this  is  true  our  experiments  first  showed  by 
the  magnetizing  effect  which  the  solenoid  had 
upon  the  needle  placed  within  it,  and  further,  by 
the  tendency  of  the  floating  magnetic  needle  to 
take  up  a  position  at  right  angles  to  a  current 
passing  in  a  north  or  soutli  direction  either  above 
or  below  it.  That  the  magnetic  field  thus  gener- 
ated by  the  current  has  a  definite  north  and  south 
pole,  which  will  be  later  shown  is  dependent  upon 
.the  direction  in  which  the  current  flows  in  the 


MAGNETISM  AND  ELECTROMAGNETISM. 


wire,  was  proved  by  the  fact  that  one  end  of  the 
solenoid  repelled  one  end  of  the  needle,  while  it 
attracted  the  other,  just  as  did  another  mag- 
netized needle — this  being  the  test  of  magnetic 
polarity. 

It  has  also  been  shown  that  a  piece  of  hard 
tempered  steel,  and  to  a  less  extent  cast  iron  and 
even  wrought  iron  which  has  become  somewhat 
hardened  either  through  drawing  or  forging  or  too 
rapid  cooling  from  a  high  temperature,  retained 
the  magnetism  indefinitely  which  had  been  im- 
parted to  it  by  the  magnetizing  current,  but  that 
the  magnetism  of  the  solenoid,  as  well  as  that  of 
soft  annealed  iron  surrounded  by  a  solenoid,  lost 
its  magnetism  the  moment  the  flow  of  current 
ceased.  These  two  phenomena  give  rise  to  two 
classes  of  magnets,  viz.,  permanent  and  electro- 
magnets, which  differ  from  each  other  only  in 
the  fact  that  in  one  case  magnetism  when  once 
produced  continues  practically  unchanged  after 
the  magnetizing  current  has  been  withdrawn,  and 
in  the  other  it  is  wholly  dependent  upon  the  con- 
tinuance of  the  current  for  its  existence,  and  the 
strength  of  the  magnetism  varies  with  every  in- 
stantaneous change  of  the  strength  of  the  current. 

Since  magnetism  is  produced  whenever  an  elec- 
tric current  flows  through  a  conductor,  and  in  the 
case  of  the  electromagnet  varies  instantaneously 
with  the  variations  in  that  flow,  it  is  readily  sug- 
gested that  the  two,  electricity  and  magnetism, 
are  closely  related  and  may  follow  somewhat 
similar  laws,  and  experiment  has  demonstrated  the 
correctness  of  this  idea. 

While  from  the  fact  that  a  permanent  magnet 
continues  to  be  magnetic  even  after  the  magnetiz- 
ing force  is  withdrawn  we  do  not  associate  the 


56  ELECTRIC    RAILWAY   MOTORS. 

same  idea  of  flow  in  a  magnet  that  we  do  in  the 
case  of  an  electric  current,  and  while  there  really 
may  be  no  flow  or  motion  of  the  thing  which  we 
may  for  the  want  of  a  better  name  call  the  "mag- 
netic fluid,"  still  the  greatest  advance  that  has 
ever  been  made  in  the  science  of  electricity  (of 
which  magnetism  is  a  most  important  part)  was 
due  to  this  conception  that  an  actual  flow  of  force 
does  take  place  in  the  magnet,  its  direction  being 
from  the  north  pole  through  the  air  to  the  south 
pole,  and  thence  through  the  magnet  back  again 
to  the  north  pole.  This  idea  involved  the  idea  of 
a  magnetic  circuit  similar  to  that  of  the  electric 
circuit,  which  must  contain  resistances.  And,  as 
in  the  electric  circuit,  in  order  to  maintain  the  flow 
of  current  there  must  be  some  pressure  to  force 
the  fluid  through  these  resistances.  It  would 
logically  follow  from  these  assumptions  that  if  a 
certain  flow  could  be  forced  to  take  place  against 
a  given  resistance  by  a  given  pressure,  a  greater 
flow  could  be  maintained  through  the  same  resist- 
ance by  a  greater  pressure,  and  we  would  have 
for  magnetism  another  Ohm's  law  expressing  the 
relation  between  the  amount  of  flow  (strength  of 
magnetism),  the  pressure,  and  the  resistance  offered 
to  the  flow.  Experiment  has  fully  verified  this 
hypothesis,  and  we  have  the  law  of  magnetism  that 
the  strength  of  a  magnet  is  equal  to  the  pressure 
divided  by  the  resistance  of  the  circuit.  While 
the  pressure  in  the  flow  of  water  is  usually  spoken 
of  as  hydrostatic  pressure,  and  that  in  the  flow  of 
electricity  is  called  electromotive  force,  the  pressure 
which  causes  magnetism  in  a  magnetic  circuit  is 
called  magnetomotive  force. 

It  has  already  been  stated,  and  the  experiments 
illustrated  in  Figs.  7  and  8  (pp.  49  and  50)  have 


MAGNETISM  AND  ELECTROMAGNETISM.  57 

shown,  that  the  magnetic  field  produced  by  a  cur- 
rent flowing  through  a  solenoid  consisting  of  two 
turns  of  a  wire  is  twice  as  strong  as  that  produced 
by  its  flowing  around  a  solenoid  consisting  of  but 
one  turn.  It  has  also  been  stated,  and  it  is  equally 
true,  that  the  magnetizing  effect  of  a  coil  of  wire 
of  any  number  of  turns  will  be  doubled  if  the  cur- 
rent in  amperes  flowing  through  the  wire  is 
doubled,  and  it  will  be  three  times  as  strong  if 
the  current  is  increased  threefold.  The  law  of 
the  magnetizing  effect  of  a  solenoid  or  hollow  coil 
of  wire  may  therefore  be  stated  as  follows  :  It  is 
proportional  to  the  current  flowing  and  to  the 
number  of  times  it  flows  through  or  around  the 
space  which  constitutes  the  magnetic  field.  Or 
in  other  words,  it  is  proportional  to  the  product  of 
the  amperes  multiplied  by  the  number  of  turns 
or  convolutions  in  the  solenoid.  Since  an  electric 
current  is  always  measured  in  amperes,  and  a  coil 
of  wire  may  be  definitely  described  by  the  number 
of  turns  of  which  it  is  composed,  it  is  a  convenient 
way  of  expressing  the  magnetizing  effect  of  the 
combination  of  the  two  by  the  product  of  these 
two,  and  the  magnetic  effect  produced  by  a  current 
of  one  ampere  flowing  around  a  coil  consisting  of  a 
single  turn  of  wire,  usually  called  an  "ampere 
turn,"  has  been  adopted  as  the  unit  of  magneto- 
motive force.  Thus  the  magnetomotive  force  of 
a  solenoid  may  be  said  to  be  that  of  100  ampere 
turns.  It  matters  not  how  these  100  ampere 
turns  are  made  up — whether  a  current  of  1 
ampere  flows  through  a  coil  of  100  turns,  2 
amperes  through  50  turns,  25  amperes  through  4 
turns  or  100  amperes  flow  through  a  coil  of  a 
single  turn — provided  only  that  the  product  of  the 
amperes  and  the  number  of  turns  in  the  coil  is 


58  ELECTRIC    RAILWAY   MOTORS. 

equal  to  100,  the  magnetomotive  force  will  always 
be  the  same. 

But  we  have  seen  that  the  quantity  of  electricity 
(amperes)  that  will  flow  through  a  circuit  is  not 
alone  dependent  upon  the  electromotive  force, 
but  is  also  dependent  upon  the  resistance  of  the 
circuit,  being  greater  where  that  circuit  is  short 
or  has  little  resistance,  and  less  where  it  is  long  or 
has  greater  resistance.  Ohm's  laws  says  that  it  is 
always  equal  to  the  electromotive  force  divided 
by  the  resistance.  This  is  equally  true  of  mag- 
netism. When  we  have  expressed  the  magneto- 
motive force  of  a  magnet,  we  have  not  yet 
defined  its  strength,  because  we  have  not  men- 
tioned the  resistance  of  the  circuit  through  which 
the  flow  is  assumed  to  take  place. 


CHAPTER  VII. 

LINES    OP   FORCE. 

WE  have  the  greatest  possible  variety  of  con- 
ductors of  electricity,  from  silver  and  copper,  which 
conduct  it  with  the  greatest  facility  and  offer  the 
least  resistance,  down  through  all  of  the  other 
metals  and  carbon  to  substances  which  are  non- 
metallic  in  character  which  offer  very  great  re- 
sistances, and  are  usually  termed  "  non-conduct- 
ors." But  of  conductors  of  magnetism — that  is, 
magnetic  substances — we  have  but  three  :  iron, 
nickel,  and  cobalt,  of  which  iron  possesses  the 
property  in  a  pre-eminent  degree.  All  other  sub- 
stances, including  the  air,  stand  about  upon  a  par 
with  each  other ;  hence  it  is  that  a  magnet  acts 
quite  as  well  through  the  top  of  a  table,  through 
a  teacup  or  saucer  full  of  water,  as  it  does  through 
the  same  space  of  air. 

If,  therefore,  we  increase  the  air  gap  between  the 
north  and  south  poles  of  a  magnet,  we  increase 
the  resistance  to  the  flow  of  magnetism,  for  the 
latter  has  to  traverse  this  length  of  non-conduct- 
ing or  poorly  conducting  substance,  and  with  an 
increased  air  space  it  will,  as  in  the  case  of  an 
increase  in  the  resistance  of  an  electric  circuit, 
require  a  corresponding  increase  of  magneto- 
motive force — or,  what  is  equivalent,  an  increase  in 
the  number  of  ampere  turns  of  wire — to  produce 


60  ELECTRIC    RAILWAY    MOTORS. 

through  this  increased  resistance  an  equal  flow  of 
magnetic  fluid. 

With  the  conception  of  a  flow  of  magnetism,  or 
"  flux,"  as  it  is  technically  called,  it  became  neces- 
sary to  have  some  unit  corresponding  to  the 
ampere  as  used  in  the  flow  of  electricity.  For 
the  magnetic  flow  or  flux  the  unit  adopted  is  "  the 


FIG.  10. 

line  of  force,"  which  is  an  imaginary  line  passing 
out  of  the  magnet  at  the  north  pole  and  into  it  at 
the  south  pole. 

Thus  in  Fig.  10,  which  represents  a  solenoid, 
the  lines  of  force  emerge  at  the  north  pole  and 
pass  around  through  the  air  and  re-enter  at  the 
south  pole.  In  the  case  of  the  solenoid  the  whole 
of  the  magnetic  circuit  is  through  the  air.  The 
resistance  to  the  flux  is  therefore  very  great,  and 
the  number  of  lines  of  force,  or,  in  other  words,  the 
strength  of  the  magnet,  will  therefore  be  very 
small. 

In  an  electric  circuit,  if  we  substitute  a  good 
conductor  for  a  poor  one,  we  will  get,  with  the 
same  electromotive  force,  more  amperes,  so  if  in 


LIIfES   OF   FORCE.  61 

the  solenoid  (Fig.  10)  we  substitute  a  bar  of  iron, 
a  good  conductor,  for  the  air  inside  of  the  coil, 
we  will  have  greatly  reduced  the  total  resistance 
of  the  circuit,  and  the  number  of  lines  of  force 
that  will  flow  around  the  magnetic  circuit  will  be 
enormously  increased,  which  means  that  we  have 


FIG.  11. 

a  magnet  of  enormously  greater  strength  from  the 
same  number  of  ampere  turns. 

We  have  here  (Fig.  11)  a  bar  electromagnet. 
But  strong  as  this  is  it  is  evident  that  in  any  bar 
magnet  at  least  one-half  the  magnetic  circuit  must 
be  in  air,  and  the  longer  the  bar  the  longer  will 
be  the  portion  of  the  circuit  which  must  traverse 
the  high-resisting  air.  If  we  bend  the  bar  around 
in  the  shape  of  a  horseshoe,  bringing  the  two 
ends  near  together,  we  may  greatly  reduce  the 
distance  which  the  lines  of  force  must  traverse 
the  air,  and  this  means  a  still  greater  number  of 
lines  that  will  be  caused  to  flow  by  the  same 
number  of  ampere  turns.  Thus  in  Fig.  12  the  N. 
and  S.  poles  are  brought  close  together,  so  that 
the  air  space  between  them  is  very  short.  The 
lines  emanating  from  the  face  of  the  N.  pole  and 
entering  the  face  of  the  S.  pole  will  therefore 
be  very  dense — much  denser  than  was  the  case  in 
Fig.  11,  where  the  iron  bar  was  the  same  length 


62 


ELECTRIC   RAILWAY    MOTORS. 


and  was  excited  by  the  same  number  of  ampere 
turns. 

In  making  these  sketches  to  any  given  scale 
there  is,  of  course,  a  limit  to  the  number  of  lines 
of  force  that  we  can  draw.  We  can  draw  a  cer- 
tain number,  but  there  is  no  room  for  more. 

The  same  conditions 
exactly  exist  as  regards 
the  number  of  actual 
lines  of  force  that  can 
be  made  to  thread 
through  any  given  bar 
of  iron.  Up  to  a 
certain  point  the  num- 
ber of  lines  remains 
very  closely  propor- 
tional to  the  magnet- 
izing  force  (ampere 
turns)  divided  by  the 
magnetic  resistance,  but  a  limit  is  finally  reached 
beyond  which  the  increase  of  ampere  turns  has 
very  little  additional  effect  upon  the  strength  of 
magnetism  produced — new  lines  of  force  are  not 
added,  siriiply  for  the  same  reason  that  we  can- 
not  draw  any  more  in  our  sketch,  viz.,  that  there 
is  no  room  for  them.  When  this  condition  is 
reached,  the  iron  is  said  to  be  "saturated." 

We  have  heretofore  spoken  of  these  lines  of 
force  as  purely  imaginary  lines.  They  have,  how- 
ever, a  more  real  existence  than  this,  for  they  can 
be  traced  or  made  visible  in  various  ways.  If  a 
plate  of  glass  be  sprinkled  with  fine  iron  filings, 
and  then  held  close  to  a  magnet  and  be  gently 
tapped  so  as  to  allow  the  particles  of  iron  to  take 
up  any  position  they  desire,  they  will  arrange 
themselves  in  curved  lines  emanating  from  the 


THE   CLOSED   MAGNETIC    CIRCUIT.  63 

north  pole  and  re-entering  the  south  pole,  which 
correspond  in  length  and  direction  with,  and,  in 
fact,  are,  the  visible  representatives  of  what  we 
have  been  speaking  of.  They  may  also  be  traced 
with  a  small  compass  needle,  which,  in  whatever 
position  it  may  be  held  with  reference  to  the 
magnet,  will  have  exactly  the  same  direction  as 
the  line  of  force  which  passes  through  it  has  at 
that  place.  Thus  a  compass  neeple  points  in  a 
north  and  south  direction,  simply  because  all  lines 
of  force  passing  between  the  two  poles  of  the 
earth  have  a  north  and  south  direction.  If,  how- 
ever, we  bring  another  magnet  near  the  needle,  the 
lines  of  force  emanating  from  it  will  overpower 
those  of  the  earth's  magnetic  poles,  and  the  needle 
will  take  up  a  position  in  accordance  with  the 
stronger,  or  rather  in  a  position  which  is  a  compro- 
mise between  the  two. 

THE    CLOSED    MAGNETIC   CIRCUIT. 

By  reference  to  the  lines  of  force  shown  by  the 
iron  filings  it  will  be  seen  that  they  emerge  from 
and  re-enter  the  magnet  only  at  the  poles.  We 
may  therefore  define  the  magnetic  poles  as  those 
portions  of  the  magnet  where  the  lines  of  force . 
emerge  from  and  re-enter  the  magnet.  We  have 
also  seen  that  as  we  decrease  the  air  distance 
through  which  these  lines  have  to  pass,  by  bend- 
ing the  magnet  around  so  that  the  poles  come 
closer  together,  the  magnet  increases  in  strength. 
It  would  be  logical,  therefore,  to  assume  that  if 
we  brought  the  two  poles  into  actual  contact,  or,  in 
fact,  made  a  closed  ring  of  the  magnet,  we  would 
have  a  magnet  of  maximum  strength,  because  the 
air  resistance  would  be  reduced  to  nothing,  and 
such  is  really  the  case,  and  the  smaller  the  diameter 


64  ELECTRIC   RAILWAY    MOTORS. 

of  the  ring  the  stronger  will  be  the  magnet,  be- 
cause the  lines  of  force  will  have  a  less  distance  of 
iron  to  traverse,  and  hence  meet  with  less  resist- 
ance due  to  that  cause. 

But  according  to  our  last  definition  a  magnetic 
pole  is  that  surface  whence  the  lines  of  force  either 
emerge  or  where  they  enter  the  magnet.  Since 
iron  is  such  an  enormously  better  conductor  of  mag- 
netism than  the  air,  the  lines  of  force  will  continue 
in  the  iron  even  though  they  may  have  to  go  con- 
siderably out  of  the  shortest  path  to  do  so.  There 
will  in  this  case  be  no  surfaces  from  which  the  lines 
will  emerge  or  into  which  they  will  enter,  and 
therefore  there  will  be  no  poles.  If  there  are  no 
lines  of  force  external  to  the  magnet,  there  will  be 
none  to  direct  a  compass  needle,  and  the  latter 
will  not  be  deflected  as  by  an  ordinary  magnet, 
nor  will  this  ring  magnet  attract  other  particles 
of  iron  or  steel.  This  is  entirely  contrary  to  the 
popular  conception  of  a  magnet,  and  it  is  only  in 
the  more  modern  works  that  a  magnet  is  not  de- 
fined by  the  unqualified  statement  that  it  possesses 
both  north  and  south  poles  which  have  the  prop- 
erty of  attracting  to  themselves  other  magnetic 
substances.  We  have,  however,  learned  that  we 
obtain  the  strongest  magnet  with  the  least  ex- 
penditure of  energy  in  an  absolutely  closed  mag- 
netic circuit  and  by  making  that  circuit  as  short  as 
possible,  and  yet  this  strongest  magnet  has  neither 
north  pole  nor  south  pole,  nor  will  it  attract  or 
repel  other  pieces  of  iron  or  steel. 

MAGNETIC    LEAKAGE. 

It  is  seldom,  however,  that  we  can  realize  fully 
these  ideal  conditions.  Although  our  iron  ring 
may  be  of  the  softest  iron,  and  there  may  be  plenty 


MAGNETIC    LEAKAGE.  65 

of  it  to  carry  all  the  lines  of  force  that  are  gener- 
ated by  the  ampere  turns  used,  some  of  these 
lines  are  apt  to  wander  outside  the  iron,  and  to 
take  a  short  cut  across  the  air  space.  These  may 
be  readily  detected  and  their  direction  indicated 
by  the  deviation  of  the  compass  needle.  To  such 
straying  lines  the  term  "  leakage  lines  "  or  "  mag- 
netic leakage  "  has  been  given. 

Wliile  the  unbroken  ring  or  closed  magnetic 
circuit  gives  us  by  far  the  strongest  magnet  for 
the  material  and  energy  employed,  there  are  many 
uses  of  the  magnet  which  require  that  it  should 
have  polarity — that  its  lines  of  force  should  pass, 
for  a  portion  of  the  distance  at  least,  through  an 
interval  into  which  may  be  introduced  substances 
to  be  acted  upon  by  these  lines  ;  but  it  is  a  cardi- 
nal law  of  magnets  that  that  magnet  which  most 
nearly  approaches  the  closed  magnetic  circuit  will 
be  the  most  efficient.  For  this  reason  magnets, 
whether  permanent  or  electro  magnets,  are  usually 
bent  around  so  that  their  poles  approach  each 
other,  and  the  object  to  be  magnetized  is  intro- 
duced into  the  gap  between  the  two  poles.  In 
order  to  concentrate  the  lines  and  make  them  as 
dense  as  possible  in  this  gap  it  is  usual  to  wind 
the  substance  to  be  acted  upon  on  a  core  of  iron, 
or  imbed  it  in  its  mass,  and  this  is  introduced  into 
the  gap,  reducing  by  that  much  the  air  resistance. 
Of  course  all  leakage  lines,  or  those  which  do  not 
pass  through  the  path  intercepted,  are  wasted,  and 
whatever  of  current  was  required  to  generate  the 
leakage  lines  was  uselessly  expended.  Exactly 
parallel  would  be  the  case  were  we  pumping  water 
through  a  long  pipe  to  operate  at  its  other  end  a 
small  water  wheel.  If  the  pipe  were  full  of  small 
holes  along  its  length,  just  as  much  more  water 


66  ELECTRIC    RAILWAY    MOTORS. 

would  have  to  be  pumped  into  the  pipe  to  do  the 
same  amount  of  work  as  leaked  out  through  these 
holes.  -That  is  to  say,  the  water  that  leaks  out  will 
cost  us  just  as  much  to  pump,  per  gallon,  as  that 
which  issues  from  the  nozzle,  and  yet  it  does  no 
useful  work.  The  economical  man  will  therefore 
not  use  a  sieve  for  a  water  pipe,  and  the  builder 
of  magnets  will  avoid  shapes  which  tend  to  mag- 
netic leakage.  In  designing  magnets  it  is  always 
desirable  to  keep  the  two  sides — the  north  half 
and  the  south  half — as  far  away  from  each  other 
as  possible  except  at  the  poles,  so  that  the  air  gap 
between  the  latter  where  we  want  to  utilize  the 
lines  of  force  will  be  the  path  of  least  resistance, 
and  the  great  distance  between  all  other  portions 
of  the  magnet  of  different  polarity  will  offer  too 
great  a  resistance  for  lines  of  force  to  jump  across. 
Sharp  angles  or  points  should  also  be  generally 
avoided,  because  magnetism  leaks  more  readily 
from  a  point  or  angle  than  from  a  smooth  surface. 
A  magnet  of  a  circular  ring  shape  best  meets  the 
required  conditions,  although  a  strict  adherence 
to  that  form  is  not  always  practicable  or  even 
desirable. 


CHAPTER  VIII. 

POLARITY,     MAGNETISM    AND     CURRENT. 

FOR  the  purpose  of  showing  the  lines  of  force 
I  bought  for  ten  cents  a  small  horseshoe  magnet 
2|-  inches  long.  Laying  this  on  its  side  on  a  table, 
1  placed  over  it  a  piece  of  glass  which  had  been 
varnished  on  one  side  and  allowed  to  become  per- 
fectly dry.  Upon  this  I  sifted  as  evenly  as  pos- 
sible some  fine  iron  filings,  and  then  tapped  the 
plate  gently  on  the  edges  in  order  to  permit  the' 
filings  to  arrange  themselves.  The  beautiful  curves 
shown  in  Fig.  13  were  the  result.  The  glass  was 
then  carefully  lifted  from  the  magnet  and  heated 
over  a  gas  flame.  This  softened  the  varnish  so 
that  the  filings  were  stuck  to  the  plate,  and  when 
the  varnish  had  hardened  again  were  preserved 
for  the  making  of  this  cut.  Fig.  13  shows  the 
lines  of  force  emanating  from  this  magnet  when 
the  armature  or  keeper  is  entirely  removed.  Fig. 
14  shows  the  lines  as  they  were  when  the  arma- 
ture was  removed  about  one-third  of  an  inch  from 
the  poles,  and  Fig.  15  shows  the  lines  as  they  ap- 
peared when  the  polar  ends  of  the  magnet  alone 
were  presented  to  the  under  side  of  the  glass 
plate. 

We  may  look  upon  these  lines  of  force  as  so 
many  elastic  bands  or  strings  by  which  the 
magnet  attaches  itself  to  other  pieces  of  iron. 

67 


68  ELECTRIC    RAILWAY    MOTORS. 

When  the  iron  is  in  actual  contact  with  the  poles 
of  the  magnet,  it  is  bound  to  the  latter  by  a  great 
number  of  these  strings.  When  we  endeavor  to 
pull  the  iron  away,  we  have  to  pull  against  the 


FIG. 


combined  elasticity  of  all  these  strings.  The  mo- 
ment we  succeed  in  pulling  it  the  slightest  distance 
from  the  magnet  a  great  many  of  these  strings 
snap  or  pull  out  of  the  iron  and  disappear  in  the 
magnet  just  as  india-rubber  strings  would  if  they 
came  out  of  a  hollow  tube  and  were  attached  to 
the  piece  of  iron  we  were  trying  to  pull  away.  As 
we  remove  the  iron  still  farther  more  arid  more  of 


POLAEITY,  MAGNETISM    AND   CURRENT.  69 

these  elastic  strings  or  bands  snap,  until  the  iron 
is  removed  beyond  the  attraction  of  the  magnet, 
when  it  may  be  said  that  all  of  the  bands  have 
been  snapped. 

Reversing  the  operation  by  gradually  approach - 


FIG.  14. 


ing  a  piece  of  iron  to  the  poles,  we  will  have  to 
draw  upon  our  imagination  somewhat  for  an 
equally  good  illustration.  As  it  comes  within  the 
attraction  of  the  magnet  first  one  or  two  elastic 
bands  jump  out  of  the  north  pole,  thread  their 
way  through  the  iron  and  attach  themselves  to 
the  south  pole.  With  a  nearer  approach  a  great 


70  ELECTRIC    RAILWAY   MOTORS. 

many  more  do  the  same  thing  and  pull  the  iron  to 
the  poles  with  all  the  force  of  their  elasticity,  and 
finally  as  the  iron  comes  nearer  they  come  out 
with  a  rush,  and  with  their  combined  pull  hold 


FIG.  15. 

the  iron  to  the  poles  with  the  greatest  force  of 
which  that  particular  magnet  is  capable. 

Now  a  clear  conception  of  the  behavior  of  these 
lines  of  force  is  indispensable  to  an  intelligent 
understanding  of  the  theory  of  the  dynamo  and 
the  motor,  and  it  is  for  this  reason  that  so 
much  space  has  been  devoted  to  the  subject. 
Do  not  be  deceived  with  the  idea  that  these 


POLARITY.  71 

lines  of  force  are  solely  of  theoretical  interest. 
We  discussed  them  at  first  as  though  their  exist- 
ence was  purely  imaginary.  Then  we  showed  by 
means  of  the  iron  filings  and  the  photographs  that 
they  really  do  exist.  Next  we  discussed  their 
behavior  in  a  somewhat  theoretical  manner,  and 


FIG.  16. 

shortly  we  will  show  how  upon  this  behavior 
depends  entirely  the  action  of  both  the  dynamo 
electric  machine  and  the  electric  motor.  But 
before  taking  up  this  latter  task,  which,  to  make 
easily  intelligible,  so  much  has  been  said  by  way 
of  preparation,  a  few  words  must  be  added  as  to 
the  effect  which  the  direction  of  flow  of  the  cur- 
rent in  the  solenoid  has  upon  the  polarity  of  the 
resulting  magnet. 

POLAEITT. 

It  may  be  stated  at  once  that  the  way  in  which 
the  wire  of  a  solenoid  is  wound  has  absolute^ 
nothing  to  do  with  which  end  of  the  inclosed  iron 
bar  will  be  the  north  pole  and  which  the  south, 
but  all  depends  upon  the  direction  in  which  the 
current  flows  around  it. 

If  in  looking  at  the  end  of  a  coil  the  current 
flows  around  it  in  the  direction  of  the  hands  of  a 
clock,  that  end  will  be  a  south  pole  (Fig.  16).  If 
the  current  is  flowing  in  the  opposite  direction  to 
that  pursued  by  the  hands  of  a  clock,  or  from 


OF  THE 

UNIVERSITY 


XS 

Y! 

^r 


72  ELECTEIC    RAILWAY    MOTORS. 

right  over  the  magnet  to  left,  that  end  will  be  a 
north  pole  (Fig.  17).  It  is  therefore  merely  a  matter 
of  convenience  whether  we  wind  a  magnet  right- 
handed  or  left-handed  ;  we  can  make  either  end  a 
north  pole  and  the  other  a  south  pole  by  simply 
connecting  the  ends  of  the  coil  with  our  circuit  so 
that  the  current  will  flow  around  the  magnet  in 
the  proper  direction,  and  if  at  any  time  we  wish 


FIG.  17. 

to  reverse  the  poles  of  the  magnet  we  simply  have 
to  reverse  our  connections.  It  is  well  to  bear  this 
in  mind,  for  there  is  a  popular  fallacy  that  the 
direction  of  winding  the  magnet,  right-handed  or 
left-handed,  determines  which  end  will  be  north 
and  which  south,  but  as  a  matter  of  fact  it  has 
nothing  to  do  with  it. 

MAGNETISM    AND    CURRENT. 

For  the  purpose  of  illustrating  the  part  which 
the  lines  of  force  (magnetism)  play  in  the  genera- 
tion of  current  I  went  to  a  blacksmith's  shop  and 
cut  off  a  piece  of  |-inch  round  iron  5£  inches 
long.  This  I  heated  and  bent  into  the  shape  of  a 
hairpin  (A,  Fig.  18),  bringing  the  ends  to  within  1^ 
inch  of  each  other.  I  then  cut  off  another  piece 
from  the  same  rod  and  bent  its  two  ends  upward 
at  right  angles  (B,  Fig.  18),  so  that  the  distance 
between  these  two  ends  was  the  same-  as  between 
the  ends  of  A.  The  ends  of  both  A  and  B  were 


MAGNETISM   AND    CIHRRENT. 


then  filed  smooth,  so  that  when  placed  together 
the  surfaces  rested  flatly  against  each  other.  Any 
blacksmith  would  probably  have  done  this  job  for 
me  for  twenty-five  cents. 

I  next  made  two  paper  spools,  each  an  inch  long, 
by  wrapping  several  thicknesses  of  manilla  paper 
around  a  stick  whittled  to  about  the  same  diame- 
ter as  my  iron,  and  forcing 
onto  this  paper  cylinder  two 
washers  made  of  heavy  card- 
board, and  pasting  the  up- 
turned ends  of  the  paper 
cylinder  to  the  outside  sur- 
faces of  these  washers,  so  as 
to  hold  them  in  place.  Then, 
while  the  spools  were  still  on 
the  stick,  I  wound  on  them 
tightly  and  as  evenly  as  possi- 
ble layer  after  layer  of  insu- 
lated wire  until  the  spools 
were  full.  I  counted  the  num- 
ber of  turns  on  the  first  spool,  and  it  happened  to 
be  382  turns.  I  wished  both  coils  to  be  as  nearly 
alike  as  possible,  so  in  winding  the  second  spool 
I  put  on  just  the  same  number  of  turns.  Then, 
slipping  the  spools  off  of  the  stick,  I  slipped  one 
on  each  leg  of  my  bent  iron  rod  A  until  about 
a  quarter  of  an  inch  or  less  of  the  ends  protruded  ; 
one  end  of  each  of  the  coils,  having  been  cleaned  of 
its  insulation,  were  twisted  together  and  the  other 
ends  were  connected  to  the  battery.  The  connec- 
tions of  the  coils  with  each  other  were  such  that, 
in  whichever  way  the  current  passed,  when  we 
looked  at  the  two  poles  it  would  be  clockwise 
around  one  and  counter  clockwise  around  the  other. 
Immediately  the  current  began  to  flow  in  the  coils 


74  ELECTEIC    RAILWAY   MOTORS. 

the  hairpin,  or  bent  iron  A,  became  a  most  power- 
ful magnet,  and  upon  bringing  the  ends  of  B  in 
contact  with  its  poles  it  attracted  it  with  great 
force.  Although  the  iron  A  weighed  less  than  a 
quarter  of  a  pound,  it  sustained  a  weight  of  about 
ten  pounds  attached  to  the  armature  B.  That 
such  a  small  amount  of  iron  could  support  such  a 
weight  would  seem  almost  incredible  to  one  who 
had  not  witnessed  it,  and,  in  fact,  would  have  been 
utterly  impossible  with  a  permanent  magnet  of  the 
same  weight.  On  breaking  the  current  the  mag- 
netism disappeared  at  once,  as  has  already  been 
explained.  It  was  found,  however,  that  it  would 
still  hold  up  a  steel  penpoint  or  two,  showing  that 
its  magnetism  was  not  entirely  lost.  This  residual 
magnetism,  as  it  is  called,  was  probably  due  to  the 
fact  that  the  iron  had  become  somewhat  hardened 
either  by  the  hammering  it  was  subjected  to  on 
the  anvil  or  by  too  rapid  cooling  after  it  came 
from  the  forge.  After  it  had  been  left  for  twenty- 
four  hours  without  current,  however,  the  residual 
magnetism  had  become  so  small  that  it  would  no 
longer  support  even  the  smallest  piece  of  iron 
accessible,  although  slight  traces  of  polarity  were 
detectable  on  presenting  the  two  ends  successively 
to  one  end  of  the  floating  needle.  These  tests, 
therefore,  showed  that  it  fairly  answered  all  the 
requirements  of  a  good  electromagnet. 


CHAPTER  IX. 

ELECTROMAGNETIC     INDUCTION. 

I  NEXT  constructed  a  paper  spool  on  the  arma- 
ture -Z?,  similar  to  those  placed  on  the  legs  of  A, 
and  wound  it  as  full  as  I  could  get  it  of  insulated 
wire.  I  counted  the  number  of  turns  and  found 
it  to  be*  421.  I  may  say  here  that  all  of  these 
dimensions  were  accidental,  and  are  only  given  to 
show  what  actual  results  were  obtainable  from 
them. 

The  object  of  placing  the  coil  on  the  short  piece 
-Z?,  which  we  will  hereafter  designate  as  the  arma- 
ture, was  to  show  what  effect  the  snapping  of  the 
lines  of  force  which  thread  a  solenoid,  or  their 
sudden  appearance  in  the  same,  would  have  upon 
the  solenoid.  It  is  evident  that  if  no  current  be 
traversing  the  coils  on  A  there  will  be  no  lines  of 
force  traveling  around  them.  If,  however,  we 
place  B  in  contact  with  A,  we  have  practically  a 
closed  magnetic  circuit,  and  if,  after  having  de- 
tached one  of  the  wires  from  the  battery,  we  touch 
it  to  its  binding  post,  the  full  strength  of  the 
magnet  will  be  instantaneously  developed,  all  of 
the  lines  of  force  of  which  our  apparatus  is  capable 
will  be  instantaneously  developed  in  A,  and  will 
rush  out  of  the  north  pole,  thread  their  way 
through  the  armature  -B,  which  is  the  core  of  our 
solenoid,  and  enter  the  magnet  again  at  the  south 
pole. 


76  ELECTRIC    RAILWAY   MOTORS. 

If  we  now  break  our  electric  current  again,  the 
lines  of  force  traversing  the  magnet  and  the  arma- 
ture coil  will  be  as  suddenly  snapped  and  disappear, 
the  result  being  the  same,  though  more  effective, 
perhaps,  as  if  the  armature  B  were  suddenly  jerked 
away  from  the  magnet  while  the  latter  retained  its 
full  magnetic  properties.  To  discover  the  effect 
of  the  sudden  introduction  within  or  withdrawal 
from  the  armature  coil  of  these  lines  of  force  let 
us  connect  its  two  ends  with  our  solenoid  (Fig.  2, 


FIG.  19. 

page  35).  Next  take  a  very  small  needle  that  has 
been  previously  magnetized  and  suspend  it  at  its 
center,  so  that  it  will  hang  horizontally.  Use  a 
coarse  spider-web  for  suspension  if  possible,  as  even 
the  finest  thread  is  a  little  stiff  and  has  a  twist  which 
will  interfere  more  or  less  with  the  action  we  are 
looking  for.  Hold  the  solenoid  up  to  the  needle  so 
that  the  latter  projects  for  about  one-third  of  its 
length  into  the  solenoid.  If  one  of  the  battery 
wires  is  disconnected  from  the  battery,  make  the 
connection  by  touching  it  to  its  binding  post. 
This,  as  we  have  seen,  will  cause  a  rush  of  lines  of 
force  through  the  armature  core.  Note  the  be- 


ELECTROMAGNETIC    INDUCTION,  77 

havior  of  the  needle  as  this  rush  occurs.  It  will 
give  a  sudden  kick,  either  outwardly  or  inwardly, 
showing  that  the  solenoid  has  momentarily  exerted 
upon  it  either  a  force  of  attraction  or  one  of  repul- 
sion. But  it  is  only  momentarily,  for  if  the  condi- 
tions remain  the  same,  the  needle,  after  swaying 
back  and  forth  a  few  times,  will  come  to  rest  again 
in  exactly  the  same  position  that  it  assumed  before 
the  lines  of  force  traversed  the  armature  core. 
The  lines  of  force  are  still  there,  but  there  is 
neither  attraction  nor  repulsion  of  the  solenoid. 
Now  break  the  battery  circuit  so  as  to  suddenly 
withdraw  the  lines  of  force.  Another  kick  will  be 
noticed  in  the  needle,  but  in  the  opposite  direction. 
If  the  solenoid  exerted  an  impulse  of  attraction 
when  the  lines  of  force  passed  into  the  armature 
core,  it  will  exert  an  impulse  of  repulsion  when  they 
are  suddenly  withdrawn.  Next  reverse  the  ends  of 
the  armature1  and  repeat  the  experiment  without 
changing  the  position  of  the  solenoid  or  its  con- 
nections. In  the  reversed  position  of  the  arma- 
ture the  end  that  was  before  in  contact  with  the 
north  pole  of  the  magnet  will  be  in  contact  with 
its  south  pole,  and  that  which  was  in  contact  with 
the  south  pole  will  be  against  the  north  pole,  so 
that  the  lines  of  force  as  they  enter  and  withdraw 
in  the  same  directions  with  regard  to  the  magnet 
have  opposite  directions  with  respect  to  the  coil. 
As  they  enter,  the  solenoid  will  be  found  to  repel 
and  to  attract  where  they  withdraw. 

Now  modify  the  experiment  a  little.  While  the 
magnet  remains  excited  jerk  off  the  armature  and 
then  replace  it.  Exactly  the  same  effect  will  be 
produced  upon  the  needle  by  the  solenoid  as  before 
when  the  current  was  alternately  broken  and 
closed.  Next  disconnect  the  solenoid,  and  connect 


78  ELECTRIC    RAILWAY   MOTORS. 

in  its  place  in  the  armature  circuit  the  flat  coil  (Fig. 
6,  see  page  41),  which  we  employed  in  our  galvan- 
ometer. Hold  this  directly  beneath  the  needle 
with  its  wires  parallel  with  the  latter.  Upon  break- 
ing and  making  the  battery  circuit  or  pulling  off 
or  putting  on  the  armature  we  will  find  that  the 
needle  receives  momentary  impulses  which  cause 
it  to  deviate  alternately  to  the  east  and  to  the 


FIG.  20. 

west.  As  with  the  solenoid,  the  effect  is  only 
momentary  and  not  sufficient  in  the  present  in- 
stance to  cause  the  needle  to  swing  far,  but  by  tim- 
ing the  makes  and  breaks,  remembering  that  they 
give  impulses  in  opposite  directions,  the  needle  may- 
be caused  to  swing  through  gradually  increasing 
arcs,  and  finally  to  rotate  completely  around  on  its 
support. 

We  will  have  recognized  before  this  that  the 
action  of  both  the  solenoid  and  flat  coil  upon  the 
needle  was  due  to  an  electric  current  caused  by 
the  sudden  introduction  and  withdrawal  of  the 
lines  of  force  through  the  armature  coil,  and  that 
the  direction  of  the  resulting  current  changed  as 


ELECTROMAGNETIC   INDUCTION.  79 

the  number  of  the  lines  of  force  threading  the 
coil  is  increasing  or  decreasing.  In  fact,  had.  we 
a  machine  by  which  the  armature  could  be  rapidly 
approached  to  or  removed  from  the  magnet  poles 
we  would  have  an  alternating  current  generator 
producing  currents  in  the  armature  circuit  exactly 
similar  to  those  employed  in  lighting  by  alternat- 
ing currents,  and  if,  further,  we  had  a  device  by 
which  the  reverse  currents  after  they  are  generated 
could  be  changed  in  direction  to  correspond  with 
those  which  both  precede  and  follow  them,  we 
would  have  in  all  respects  a  direct  current  genera- 
tor. In  fact,  almost  before  we  have  been  aware  of 
it,  we  have  actually  developed  experimentally  an 
electrical  generator.  It  now  only  remains  to 
develop  the  details  by  which  the  current  generated 
is  rendered  continuous  in  one  direction  instead  of 
alternating,  and  practically  steady  instead  of  pulsa- 
tory, as  it  would  be  were  the  currents  we  have  just 
generated  all  sent  in  the  same  direction.  We  have 
also  discovered  that  the  electromotive  force  is  not 
due  to  the  actual  number  of  lines  threading  the 
coil,  for  the  same  effect  was  produced  when  there 
were  no  lines — when  the  magnet  was  not  excited — 
as  when  there  was  the  greatest  number — that  is 
to  say,  there  was  no  effect  in  either  case,  but  the 
current  flowed  only  when  the  number  of  lines  was 
changing.  The  rule  is  that  the  potential  difference, 
which  gives  rise  to  the  current,  is  proportional  not 
to  the  number  of  lines  included  by  the  coil,  but  to 
the  rate  of  change  of  the  number  of  lines.  In 
our  experiments  it  was  an  almost  instantaneous 
change  from  no  lines  to  the  full  number  we  were 
able  to  generate,  and  from  that  number  to  none 
again. 


80  ELECTRIC    RAILWAY   MOTORS. 


THE    CONTINUOUS    CURRENT   DYNAMO. 

Iii  the  dynamo  of  to-day  a  much  more  conven- 
ient method  of  varying  the  number  of  lines  in- 
cluded in  the  coil  is  obtained  by  revolving  that 
coil  around  an  axis  in  a  uniform  magnet  field. 

In  Fig.  20  we  have  a  representation  of  a  single 
turn  of  wire  revolving  around  one  of  its  sides,  as 
an  axis  in  a  uniform  magnetic  field.  In  the  posi- 
tion shown  none  of  the  arrows  will  be  embraced 
by  the  coil,  but  as  we  revolve  it  in  either  direction 
it  gradually  will  allow  more  and  more  lines 
of  force  to  pass  through  it,  until  it  arrives  at 
a  position  at  right  angles  to  the  one  shown,  when 
it  will  embrace  the  maximum  number,  but  in 
this  position  its  motion  will  be  for  a  moment 
parallel  with  the  lines  of  force,  so  that  for  a  very 
small  portion  of  its  revolution  near  this  position 
it  will  cut  no  more  and  no  fewer  lines.  Its  rate 
of  cutting  lines  at  this  point  being  zero,  no  electro- 
motive force,  and  consequently  no  current,  will 
be  generated.  As  it  proceeds  around  through 
another  right  angle  the  number  of  lines  which 
the  loop  will  include  diminishes,  gradually  at 
first,  but  more  and  more  rapidly,  until  the  position 
of  the  loop  is  directly  opposite  that  shown  in  the 
cut,  when  it  again  becomes  parallel  with  the  lines 
and  for  a  moment  includes  no  lines,  but  as  it  passes 
this  position  the  loop  turns  its  other  side  to  the 
north  pole,  and  commences  to  take  in  lines  from 
the  opposite  side — that  is  to  say  that  with  respect 
to  the  loop  the  direction  of  the  lines  is  reversed. 
At  this  point  the  rate  of  change  of  the  number 
of  lines  embraced  by  the  coil  is  a  maximum, 
because  at  one  instant  there  were  a  few  lines 
going  through  the  coil  in  one  direction,  and  at  the 


THE    CONTINUOUS    CURRENT   DYNAMO.  81 

next  there  was  the  same  number  going  through 
in  the  opposite  direction,  or  there  were  just  that 
many  less  than  nothing  going  through  in  the 
original  direction  the  second  moment.  The 
greatest  rate  of  change  in  the  number  of  lines 
embraced  by  the  coil  that  can  possibly  occur 
takes  place  at  this  part  of  the  revolution,  and 
therefore  at  this  point  in  its  path  the  greatest 
electromotive  force  is  generated.  From  this 
point  to  the  vertical  position  of  the  loop,  at  right 
angles  to  the  lines  of  force,  the  rate  of  change  be- 
comes slower  and  slower,  and  the  electromotive 


force  less,  until  the  loop  arrives  at  the  latter  posi- 
tion, when  for  a  moment  there  is  no  change,  since 
its  motion  is  for  the  time  again  parallel  with  the 
lines  of  force.  No  electromotive  force  is,  therefore, 
developed  at  this  point  in  the  revolution,  but 
from  here  to  the  original  position,  shown  in  Fig.  20, 
the  rate  of  change  gradually  increases  again,  until 
it  becomes  a  maximum  once  more  in  the  position 
shown.  It  will  be  observed,  therefore,  that,  as 
the  coil  is  revolved  between  the  two  poles  of  the 
magnet,  the  electromotive  force  generated  twice 
reaches  a  maximum,  once  when  the  coil  is  in  the 
position  shown,  and  again  when  180°  from  this 
position,  and  twice  becomes  zero,  viz.,  when  it 


82  ELECTEIC    RAILWAY   MOTORS. 

is  in  the  two  positions  at  right  angles  to  this 
plane.  In  each  case,  as  the  electromotive  force 
passes  through  zero,  the  current  resulting 
changes  its  direction,  so  that  in  each  revolution 
of  the  coil  the  current  will  flow  half  the  time 
through  the  outside  circuit  from  A  to  J5,  and  dur- 
ing the  other  half  in  the  contrary  direction,  from 
JSto  A. 

The  more  usual  way  of  explaining  this  genera- 
tion of  electromotive  force  is  to  speak  of  the  rate 
at  which  a  wire  represented  in  section  by  the  dot 
Cy  Fig.  21,  cuts  the  lines  of  force  when  revolved 
in  a  circular  path  A  E  D  G  in  a  uniform  mag- 
netic field  represented  by  the  parallel  lines.  Re- 
ferring to  the  figure,  when  the  wire  is  at  (7,  it  is 
traveling  for  the  moment  parallel  with  the  lines  of 
force,  and  therefore  cutting  none  and  generating 
no  electromotive  force.  As  it  proceeds  around 
from  left  to  right  it  cuts  these  lines  more  and  more 
rapidly,  until  at  E  it  is  moving  at  right  angles  to 
them,  where  it  cuts  them  at  the  maximum  rate  of 
its  course.  At  this  part  of  its  path  the  highest 
electromotive  force  is  generated.  From  E  to  D 
it  cuts  them  less  and  less  rapidly,  until  it  arrives  at 
D,  where  its  motion  is  again  parallel  to  the  lines 
and  no  electromotive  force  is  generated.  From  D 
to  6r  the  rate  again  increases  and  from  G  to  C 
decreases,  but  the  direction  of  the  current  during 
this  half  of  its  excursion  is  in  the  opposite  direc- 
tion to  that  resulting  from  its  course  in  the  first 
half — the  changes  of  direction  of  the  electro- 
motive force  or  pressure  upon  which  the  current 
and  its  direction  depend  taking  place  as  the  wire 
passes  through  the  positions  where  it  cuts  no 
lines,  called  the  neutral  positions,  A  and  D. 

While  the  same  results  are  reached  by  explain- 


THE    CONTINUOUS   CURRENT   DYNAMO.  83 

ing  the  action  of  a  moving  wire  in  a  magnetic 
field  in  this  way  as  in  the  other,  it  is  not  strictly  a 
correct  explanation,  for  according  to  it  the  gener- 
ation of  electromotive  force  is  made  to  depend 
upon  the  actual  cutting  of  the  lines  of  force  by  the 
moving  wire.  We  have  seen  that  this  is  not  a 
fact,  for  in  our  experiment  with  the  electromagnet 
(Fig.  19)  we  found  that  with  our  coil  on  B  per- 
fectly stationary  we  generated  an  electromotive 


FIG.  22. 

force  simply  by  making  and  breaking  the  battery 
connection  with  .the  magnet  coils,  thereby  rapidly 
changing  the  number  of  lines  that  threaded  through 
the  armature  core,  from  zero  to  a  maximum,  and 
vice  versa.  In  this  case  there  was  absolutely  no 
cutting  of  lines.  But,  as  before  stated,  the  same 
results  follow  both  methods  of  explanation,  and  the 
latter,  although  strictly  speaking  not  correct,  is 
simpler,  and  for  that  'reason  will  be  used  here- 
after. 

Fig.  20  represents  an  electromagnetic  generator 
in  its  simplest  form. 

It  is  more  usual,  however,  instead  of  having  a 


84  ELECTRIC   RAILWAY   MOTORS. 

narrow  coil  revolving  around  one  of  its  sides  as  an 
axis,  to  employ  a  larger  coil  and  revolve  it  around 
an  imaginary  axis  in  its  center,  as  shown  in  Fig. 
22.  In  this  case  when  the  coil  revolves  in  the 
direction  indicated,  while  the  side  A  J3  cuts  the 
lines  in  one  direction,  the  other  side,  A  D,  cuts 
them  in  the  opposite  direction.  In  the  cut  the 
end  J9  is  represented  as  terminating  in  the  hollow 
cylinder  JB,  through  the  axis  of  which  passes  the 
other  end  of  the  coil,  also  terminating  in  a  cylin- 


FIG.  23. 

der.  Upon  these  two  cylinders  copper  brushes 
are  pressed,  to  which  are  attached  the  two  ends  of 
the  external  circuit  D  G  E. 

With  the  coil  in  the  position  shown  the  maxi- 
mum electromotive  force  is  being  generated  for 
the  reasons  already  explained,  and  the  direction  of 
the  resulting  current  will  be  as  indicated  by  the 
arrows.  When  the  coil  has  arrived  at  the  position 
shown  in  Fig.  23,  it  is  cutting  no  lines  of  force 
and  generating  no  electromotive  force,  but  imme- 
diately after  passing  this  position  it  commences  to 
cut  the  lines  again,  the  two  sides  cutting  the  lines 


THE    CONTINUOUS    CURRENT    DYNAMO.  85 

in  opposite  directions,  however,  viz.,  A  B  has 
exchanged  places  with  A  D,  the  former  cutting 
them  from  west  to  east,  if  in  looking  toward  the 
north  pole  we  be  supposed  to  be  looking  north, 
and  the  latter  now  cutting  them  from  east  to  west, 
using  the  same  points  of  the  compass.  The  cur- 
rent will,  therefore,  be  reversed,  and  will  reach  its 
maximum  strength  when  in  the  position  shown  in 


Fig.  24.  It  will  again  become  zero  and  reverse 
its  direction  when  the  coil  has  reached  a  position 
at  right  angles  to  this  ;  and  so  the  changes  will 
follow  each  other  as  the  coil  revolves,  repeating 
the  changes  with  each  revolution,  becoming  zero 
and  reversing  its  direction  each  time  the  coil  takes 
up  a  position  at  right  angles  to  the  lines  of  force, 
and  reaching  a  maximum  each  time  it  becomes 
parallel  with  them. 

We  have  here  what  may  be  termed  a  typical 


86  ELECTRIC   RAILWAY   MOTORS. 

machine  generating  alternating  currents,  viz., 
those  which  are  periodically  reversing  their  direc- 
tion. What  is  wanted,  however,  is  to  generate  a 
current  that  shall  flow  always  in  the  same  direc- 
tion in  the  outer  circuit.  It  is  evident  that  if  at 
the  moment  the  coil  arrived  in  its  neutral  position 
(Fig.  23),  when  for  one  moment  it  is  generating  no 
current  and  the  next  commences  to  generate  one 


FIG.  25. 

in  the  opposite  direction,  we  should  exchange  the 
places  of  the  two  brushes  D  and  E,  placing  E 
upon  the  cylinder  which  terminates  the  end  of  the 
wire  B,  and  D  upon  the  cylinder  (7,  and  replace 
them  again  in  their  original  positions  when  the 
coil  arrives  at  its  next  neutral  position,  the  current 
in  the  external  circuit  would  no  longer  be  reversed, 
but  would  continue  to  flow  in  the  same  direction 
throughout  the  complete  revolution  of  the  coil. 
A  simpler  way  of  accomplishing  the  same  thing, 
however,  is  at  hand. 

Suppose  the  hollow  cylinder  D,  in  Figs.  20,  22, 
23,  24  (see  pages  78-85),  be  slit  longitudinally  into 
two  equal  parts,  and  let  one  part  be  connected  to 
each  of  the  two  ends  of  the  turn  of  the  wire,  as 


THE    CONTINUOUS   CUBBENT   DYNAMO.  87 

shown  in  perspective  in  Figs.  25  and  26,  and  in 
section  to  a  larger  scale  in  Figs.  27  and  28. 

Calling  these  two  halves  m  and  ra,  if  we  place 
the  slits  at  right  angles  to  the  coil,  as  shown  in 
the  figures,  and  place  the  brushes  D  E  in  the 
positions  shown,  the  direction  of  the  current  in 
the  outer  circuit  will  be  automatically  changed 
at  the  proper  time.  In  Fig.  28  the  coil  is  in  one 
of  its  neutral  positions.  Just  before  this  D  has 
been  in  contact  with  m  and  E  with  n;  the  current 


FIG.  26. 

at  that  time  was  flowing  from  n  through  E  G-  D  to 
m.  When  the  coil  has  arrived  at  the  vertical  posi- 
tion shown  in  Fig.  28,  there  is  no  electromotive 
force  generated,  but  just  after  it  has  passed  this 
position  section  n  passes  from  under  brush  E  and 
section  m  passes  from  under  brush  D.  There- 
fore brush  E  rests  upon  section  m  and  brush  D 
upon  section  n  (Fig.  29),  just  as  the  direction  of 
the  electromotive  force  in  the  coil  changes,  so  that 
the  current  will  continue  to  flow  in  the  same  direc- 
tion in  the  circuit  E  Gr  D  as  before. 


88  ELECTRIC   RAILWAY   MOTORS. 

This  arrangement,  by  which  the  alternating 
current  is  changed  to  one  always  flowing  in  the 
same  direction,  is  termed  a  commutator,  and  the 
line  joining  the  positions  of  the  brushes  where  the 
change  of  direction  or  commutation  takes  place 
is  called  the  "  axis  of  commutation." 

We  have  already  accomplished  part  of  our  pur- 
pose, but  not  all,  for  while  the  current  now  always 
flows  in  the  same  direction,  it  is  an  exceedingly 
unsteady  one,  having  at  one  time  no  electromotive 
force  at  all  and  at  another  a  maximum.  We  must 


FIG.  27. 

have  a  more  uniform  current,  and  to  this  end  let 
us  add  another  coil  at  right  angles  to  the  first 
(Fig.  30). 

If  this  second  coil  is  added  and  the  commutator 
split  into  four  sections,  the  currents  in  both  coils 
will  be  rectified,  and  as  the  coil  b  is  in  its  neutral 
position  while  coil  c  is  generating  its  maximum 
electromotive  force,  and  vice  versa,  there  will  be 
no  time  when  the  circuit  is  without  current,  for 
while  coil  b  is  contributing  nothing,  the  other 
coil,  c,  is  doing  its  best.  Referring  to  the  cut  it 
will  be  seen  that  each  coil  will  come  into  action 
when  it  comes  within  45°  of  its  position  of  maxi- 


THE    CONTINUOUS    CURRENT   DYNAMO.  89 

mum  effect,  and  will  go  out  of  action  when  it  has 
passed  45°  beyond  that  point. 

While  in  the  position  shown  the  coil  c  is  in  a 
maximum  position,  and  section  o  is  positive  and  p 
negative.  The  current  will  therefore  flow  from 
brush  E  through  the  circuit  to  B.  The  potential 
will  diminish  until  the  coil  has  passed  through  45°. 
Then  the  sections  o  and  p  of  the  commutator  and 
the  coil  will  no  longer  be  in  connection  with  the 
brushes  and  the  outer  circuit,  and  may  be  neglected 


FIG.  28. 

for  the  next  quarter  of  a  revolution.  When  the 
segments  o  and  p  pass  from  under  the  brushes, 
segments  m  and  n  immediately  succeed  them  and 
coil  b  is  connected  to  circuit.  This  coil  is  approach- 
ing its  position  of  maximum  effect,  and  therefore 
its  potential  difference  is  increasing,  and  will  con- 
tinue to  increase  as  it  passes  through  an  angle  of 
45°,  when  it  reaches  its  maximum,  and  will  then 
decrease  as  did  coil  c  for  45°  more,  until  like  the 
other  coil  it  is  cut  out  of  circuit  by  its  commutator 
segments  passing  from  beneath  the  brushes.  Thus 
a  decreasing  electromotive  force  of  a  strength  due 
to  a  position  of  one  coil  45°  beyond  its  position  of 


90  ELECTEIC    RAILWAY    MOTORS. 

maximum  effect  is  succeeded  by  an  increasing 
electromotive  force  from  another  coil  due  to  its 
position  of  45°  in  front  of  its  position  of  maximum 
effect,  and  we  have  a  current  still  varying  in 
strength,  but  only  between  that  which  would  re- 
sult from  a  position  of  the  coils  of  maximum 
effect  and  that  which  would  result  from  a  position 
45°  removed  from  it  instead  of  one  varying  be- 
tween a  maximum  and  zero. 

If  we  double  the  number  of  coils  again  and 
divide  each  of  our  commutator  segments  into  two, 
the  fluctuations  will  become  still  less,  and  so,  by 
multiplication  of  coils  each  terminating  at  both 
ends  in  commutator  segments  which  come  under 
the  brushes  and  leave  them  at  a  less  angle  from 
jihe L  position  of  maximum^  effect,  th e  re suTfing^  cur- 
rent will  vary  between  narrower  and  narrower 
limits  and  gradually  approach  uniformity  of 
strength. 

INCREASE  OF  ELECTROMOTIVE  FORCE. 

We  observed  from  our  experiments  with  the 
solenoids  that  two  turns  affected  the  needle  more 
than  one  turn  did,  and  it  has  been  stated  that  the 
magnetizing  effect  of  a  coil  or  the  magnetomotive 
force  of  an  electromagnet  was  proportional  to  the 
product  of  the  current  flowing,  into  the  number  of 
turns  in  the  coil,  or  the  ampere  turns,  as  we  have 
called  this  product.  The  converse  of  this  is  also 
true.  If  a  coil  of  one  turn  of  wire  such  as  has 
been  discussed  heretofore  revolving  in  a  given 
magnetic  field  at  a  certain  speed  generates  an 
electromotive  force  of  say  one  volt,  a  coil  of  two 
turns  or  a  coil  of  three  turns  revolving  at  the  same 
speed  in  the  same  field  will  generate  an  electro- 


INCREASE  OF  ELECTROMOTIVE  FORCE.     91 

motive  force  of  double  or  treble  as  much.  That 
is  to  say  that  since  a  given  current  passing  two 
and  three  times  around  a  bar  of  iron  or  space  will 
generate  two  and  three  times  as  many  lines  of 
force  as  it  will  if  it  passes  around  but  once,  so  if 
a  coil  of  one  turn  cutting  the  lines  of  force  at -a 
given  rate  generates  a  certain  electromotive  force, 
the  same  wire  bent  into  a  coil  of  two  and  three 
turns  will  under  like  conditions  generate  two  and 


FIG.  29. 

three  times  as  many  volts.  Thus  if  a  coil  such  as  is 
represented  in  Fig.  31  (seepage  93)  be  substituted 
for  the  coils  of  a  single  turn  represented  in  the 
previous  illustrations,  it  will  at  the  same  speed  of 
revolution  generate  twice  as  much  electromotive 
force,  because  in  doubling  the  wire  it  is  equivalent 
to  doubling  the  rate  at  which  that  wire  cuts  the  lines 
of  force — which  alone  determines  the  electromo- 
tive force  that  will  result.  This  being  the  law, 
many  other  means  of  increasing  the  electromotive 
force  at  once  suggest  themselves.  If  we  revolve 
our  coil  faster,  its  rate  of  cutting  will  be  greater, 
or  if  we  increase  the  number  of  the  lines,  the  rate 
of  cutting  will  still  be  faster,  even  though  the 


92 


ELECTRIC    RAILWAY    MOTORS. 


speed  of  revolution  be  not  increased.  This  latter 
statement  suggests  two  other  means  of  increasing 
the  electromotive  force,  for  we  can  increase  the 
number  of  lines  of  force  in  our  field  in  two  ways 
— either  by  increasing  the  magnetomotive  force  of 
our  magnet  by  increasing  the  number  of  ampere 
turns,  or  by  decreasing  the  magnetic  resistance  of 
the  air  space  in  which  our  coils  revolve.  Since 


FIG.  30. 

our  coils  are  of  a  certain  size,  we  cannot  bring  the 
poles  of  the  magnet  closer  together,  as  we  did  in 
Fig.  12  (see  page  62),  and  still  leave  room  for  our 
coils  to  revolve,  but  we  can  wind  our  coils  on  a 
cylinder  of  iron,  which  is  the  best  conductor  of 
the  magnetic  lines  that  is  known,  and  thus  by 
greatly  reducing  the  resistance  in  this  gap  greatly 
increase  the  number  of  lines  that  our  coils  will 
cut  at  a  given  speed,  and  thus  increase  enormously 
our  electromotive  force.  And  this  method  is 
always  employed  in  dynamo  construction,  because 
it  results  in  an  enormous  saving  in  copper,  since 
with  one  turn  of  the  wire  on  an  iron  core  a  greater 
number  of  volts  will  be  generated  than  with  very 


OF  THE 

UNIVERSITT 


EDDY  CURRENTS 


many  turns  of  wire  without  the  iron  revolved  at 
the  same  speed.  Nor  is  any  expense  spared  to 
have  this  core  of  the  softest  and  best  iron  for  the 
purpose,  for  the  saving  in  other  directions  where 
the  best  iron  is  employed  in  the  armature  core 
more  than  counterbalances  the  additional  cost  of 
the  extra  quality. 


EDDY  CURRENTS  IN  ARMATURE. 

Those  who  have  seen  generator  or  motor  arma- 
tures in  process  of  construction  will  have  noticed 
also  that  they  are  not  made  of  one  solid  piece,  but 
are  built  up  of  a  great  number  of  disks  of  thin 


FIG.  31  AND  32. 

sheet  iron,  each  of  these  disks  being  insulated 
from  its  neighbors  usually  by  thin  sheets  of  paper. 
This  lamination,  as  it  is  called,  is  not  for  the 
purpose  of  increasing  the  capacity  of  the  iron  to 
carry  lines  of  force,  but  is  for  the  purpose  of  per- 
mitting the  core  to  rapidly  change  the  direction 
of  its  magnetization.  As  will  be  seen  later  on  the 
armature  becomes  a  magnet  whose  poles  always 
have  a  constant  position  with  regard  to  the  field 


94  ELECTEIC   RAILWAY   MOTORS. 

magnet  poles — that  is,  they  are  stationary  with 
regard  to  the  latter — but  since  the  armature  is  re- 
volving, they  are  constantly  changing  with  regard 
to  a  fixed  point  on  the  armature.  Thj^J^minaiipn 
greatly  facilitates  the  rapid  shifting  of  these-poles, 
which  if  retarded,  as  would  be  the  case  even  with 
the  best  iron  if  it  were  solid,  would  give  rise  to 
eddy,  or  Foucault  currents,  as  they  are  called,  in 
the  iron  itself,  which  would  be  at  the  expense 


FIG.  33. 


of  the  engine  which  drives  the  armature,  would 
contribute  nothing  in  return  to  the  output  of  the 
dynamo,  would  cause  the  armature  to  heat  up  to 
an  abnormal  degree  so  as  to  perhaps  destroy  the 
insulation  on  the  armature  wires,  and  cause  irreg- 
ularities of  working  too  numerous  to  mention  at 
tliis  point. 

Figs.  32  and  33  represent  an  armature  con- 
sisting of  two  coils  of  two  turns  wound  on  an 
iron  core  at  right  angles  to  each  other.  It 
will  be  seen  that  in  Fig.  33  when  the  armature  is 
inserted  between  the  pole  pieces  N  S  the  distance 
which  the  lines  of  force  have  to  pass  through  air 
is  reduced  to  the  two  narrow  spaces  which  need 


EDDY  CURRENTS  IN  ARMATURE.        95 

only  be  wide  enough  to  permit  the  armature  to 

revolve  rapidly  without  allowing  the  coils  to  strike 

against  the  faces  of  the  field  magnets.      Of  course 

as  the  armature  revolves  the  wires  on  its  surface 

tend  to  fly  outward,  and  sufficient  room  must  be 

allowed  to  provide  for  this.     Other  precautions  are 

taken  to  prevent  these  wires,  E  JF] 

Fig.   32,  from   flying  outward  or 

from    moving   in    any   way   from 

their    position.     In    small   motors 

and   dynamos  the   most   common 

way  to  prevent  this  is  to  bind  them 

down    tightly   to   the    core    with          pIG  34 

a   number   of   windings    of  wire. 

In  larger  machines  it  is  now  becoming  very 
common  practice,  instead  of  winding  the  wires  on 
the  outside  of  the  cylindrical  surface  of  the  core, 
to  carry  them  through  slots  cut  in  the  iron  itself, 
each  coil,  whatever  the  number  of  turns,  occupy- 
ing a  slot  by  itself. 

Fig.  34  represents  an  armature  thus  wound. 
This  method  where  the  size  of  the  machine  per- 
mits has  several  advantages,  some  of  which  are 
mechanical,  while  others  are  purely  electrical.  One 
of  the  chief  advantages  is  that  it  is  impossible  for 
the  wires  to  move,  and  another  is  that  the  air  space 
between  the  armature  and  the  pole  pieces  of  the 
field  magnet  may  be  made  considerably  smaller, 
for  it  is  evident  that  the  space  taken  up  by  the 
windings  of  the  wire  on  the  outside  of  the  arma- 
ture offers  quite  as  high  resistance  to  the  magnetic 
flow  as  does  that  additional  space  which  must 
necessarily  be  left  for  clearance. 


CHAPTER  X. 

SHIFTING    OF   THE    ABMATUEE    WIBES. 

WE  have  laid  some  stress  upon  the  injunction 
that  the  windings  of  the  armature  must  not  be 
allowed  to  move.  It  is  evident  that  if  they  are 
free  to  move  ever  so  little  it  will  be  almost  sure 
to  result  in  the  breaking  of  the  insulation  with 
which  they  are  protected,  and  this  being  destroyed, 
even  over  spaces  the  size  of  a  pin  head,  the  cur- 
rent will  pass  from  wire  to  wire  of  the  coils,  or 
from  wire  to  armature  core,  instead  of  passing 
out  through  the  commutator  and  outer  circuit, 
and  this  new  path  being  short  and  of  low  resist- 
ance, the  flow  will  be  large,  or  if  not  large  at  first 
rapidly  become  larger,  and  the  armature  burns 
out.  In  fact,  this  slight  movement  of  the  coils  is 
one  of  the  most  fruitful  causes  of  burning  out  of 
armatures. 

There  are  three  agencies  constantly  at  work 
when  either  the  dynamo  or  motor  is  in  operation 
which  tend  to  cause  movement  of  the  coils  and 
hence  their  ultimate  destruction.  One  has 
already  been  referred  to — the  tendency  of  the 
wires  to  fly  off  from  the  core  when  the  latter  is 
revolving  rapidly,  which  is  counteracted  by  bind- 
ing them  down  tightly  to  the  core  by  bands  or 
coils  of  fine  wire.  Another  is  that  when  a 
dynamo  is  doing  work,  and  the  coils  are  passing 


SHIFTING    OF   THE    ARMATURE    WIRES.  97 

rapidly  through  the  lines  of  force,  the  latter  act 
like  material  obstructions  to  their  motion  with 
the  core  and  tend  to  push  them  off  sideways.  It 
is  very  much  as  though  we  were  revolving  the 
armature  rapidly  in  a  tank  of  water  ;  considerable 
friction  would  result  between  the  water  and  the 
wires  on  the  surface  of  the  cylinder,  which  would 
tend  to  strip  the  former  from  the  latter,  and  this 
tendency  would  increase  with  the  speed.  One 
can  form  an  estimate  of  how  great  this  stripping 
force  is  when  he  realizes  that  practically  all  of  the 
force  exerted  by  the  engine  in  driving  the  arma- 
ture is  required  to  overcome  it.  That  is  to  say, 
that  when  an  engine  is  exerting  say  100  H.  P.  in 
driving  an  armature  there  is  practically  100  H.  P. 
being  exerted  upon  the  windings  of  that  armature 
tending  to  push  them  off  sideways  or  to  strip 
them  from  their  position.  This  stripping  force  is 
divided  among  the  coils,  and  increases  for  each 
coil  with  the  number  of  turns  in  the  coil.  In  the 
case  of  the  dynamo  this  friction  acts  as  a  drag 
upon  the  coils,  tending  to  prevent  them  from  pass- 
ing from  under  the  pole  pieces  of  the  magnets. 
In  the  case  of  a  motor  the  action  is  reversed,  and 
it  manifests  itself  as  a  pull  upon  the  wires  as  they 
approach  the  pole  pieces. 

It  is  bad  enough  when  this  tendency  to  strip  is 
always  in  one  direction,  for,  as  the  force  exerted  is 
constantly  varying  with  the  load  on  the  machine, 
there  is  a  tendency  for  the  coils  to  move  accord- 
ingly, which  if  allowed  to  occur  must  inevitably 
result  in  friction  between  the  wires  themselves,  or 
between  the  wires  and  the  core,  which  will  wear 
away  the  insulation  in  places  and  cause  a  short 
circuit  and  a  burn  out,  but  it  is  still  worse  where 
the  strain  comes  first  in  one  direction  and  then  in 


/ 

(•UNIVER 

V  OP 


•UNIVERSITY 


98  ELECTRIC    RAILWAY    MOTORS. 

the  opposite,  as  is  the  case  with  motors  which  are 
constantly  reversed,  as  are  street  car  motors.  One 
of  the  trials  to  which  street  car  motors  are  pecul- 
iarly subject  is  the  tugging  in  one  direction  at  the 
wires  on  the  armature  on  starting  up,  and  the  tug- 
ging at  them  again  in  the  opposite  direction  when- 
ever the  car  is  reversed,  and  it  is  much  aggravated 
if  these  operations  are  performed  too  suddenly. 
This  is  one  of  the  reasons  why  motormen  are  always 
instructed  not  to  turn  on  the  current  too  rapidly 
in  either  direction,  and  why  provision  is  made  in 
the  controlling  switch  so  that  the  current  cannot 
be  turned  on  or  off  or  reversed  at  full  strength. 
The  deterioration  of  reversing  motors  (street  car 
motors)  due  to  this  cause,  even  with  the  best  of 
care  on  the  part  of  the  motorman,  is  slow  but  sure. 

There  are  several  methods  of  obviating  this  tend- 
ency of  the  wires  to  shift,  with  which,  however, 
the  motorman  has  nothing  to  do.  One  is  that 
which  is  resorted  to  to  prevent  the  wires  from  flying 
off  tangentially,  previously  described,  of  tightly 
binding  the  coils  to  the  armature  by  metal  bands 
or  wrappings  of  wire,  and  the  other  is  by  imbed- 
ding the  coils  in  channels  or  slots  in  the  armature 
core  as  shown  in  Fig.  34  (see  page  95).  This  latter 
method,  however,  is  seldom  practicable  in  small 
motors  such  as  are  used  on  street  cars,  because  of 
lack  of  room  for  the  required  number  of  coils,  but 
in  large  generators  and  motors  of  many  hundred 
horse  power  it  is  becoming  a  favorite  method,  not 
only  on  account  of  its  efficiency  for  the  purpose, 
but  because  this  method  of  building  the  armature 
has  other  advantages  to  recommend  it. 

In  street  car  motors,  however,  where  of  all  cases 
there  should  be  the  best  possible  provision  against 
these  strains,  we  have  to  rely  upon  the  least  efficient 


SHIFTING    OF   THE    ARMATURE   WIRES.  99 

method,  viz.,  of  holding  the  wires  in  place  by  the 
binding  wires  referred  to.  The  motorman  who 
has  the  best  interests  of  his  employers  at  heart  will 
therefore  refrain  from  jerking  his  car,  for  he  will 
remember  that  these  jerks  all  come  upon  the  arma- 
ture wires  and  will  hasten  the  destruction  of  his 
machine. 

The  third  agency  which  tends  to  cause  the  wires 
to  move  from  their  position  upon  the  armature  is 
heat.  As  everyone  knows, 
metal  expands  with  in- 
crease of  temperature.  Now 
the  coils  of  an  armature  are 
wound  as  tightly  as  possi- 
ble, but  if  the  temperature 
of  the  wire  be  raised  far  ;pIG 

above  that  at  which  it  was 

wound  the  wire  will  become  appreciably  longer, 
and  the  coils,  which  were  tight  when  cool,  be- 
come loose  when  hot.  Upon  cooling  again  they 
contract,  but  this  very  expansion  and  contrac- 
tion has  caused  a  motion  of  the  various  con- 
volutions of  the  wire  relative  to  each  other  and  to 
the  core  which  may  be  more  or  less  harmful  by 
causing  abrasion  ;  but  the  heating  is  still  more 
harmful  for  the  reason  that  it  aggravates  the  other 
tendencies  toward  movement  of  the  coils  already 
mentioned,  for  if  these  strains  are  brought  to  bear 
upon  a  coil  that  is  already  loose  it  will  be  readily 
seen  how  much  more  harmful  they  may  become. 
The  only  remedy  for  this  is  to  avoid  overworking 
your  machine.  Over  this  remedy  the  motorman 
has  almost  complete  control.  Starting  up  or 
reversing  too  suddenly,  or  taking  a  heavy  load  too 
rapidly  up  a  grade,  are  all  examples  of  practices 
that  should  be  prohibited,  because  in  all  of  them 


100  ELECTRIC    RAILWAY    MOTORS. 

the  wires  are  overworked  and  likely  to  heat  even 
to  burning  out.  Running  at  a  high  speed  on  a  level 
track  is  not  overworking  the  motor,  however,  and 
may  be  indulged  in  with  impunity,  almost,  so  far 
as  the  heating  of  the  motor  is  concerned,  so  that 
it  is  much  better  to  lose  time  on  grades  and  make 
it  up  on  the  level  stretches  than  to  save  time  at  the 
expense  of  the  motor  where  the  hardest  work  is 
being  done,  viz.,  in  starting  and  in  ascending  grades 
and  going  round  curves. 

OPEN   AND    CLOSED    COIL   ARMATURES. 

In  all  of  the  preceding  cuts  where  the  armature 
is  represented  as  having  two  coils  and  four  com- 
mutator segments  it  will  be  observed  that,  after 
the  coil  has  passed  45°  from  its  position  of 
maximum  activity,  its  commutator  segments  pass 
from  under  the  brushes,  and  the  outside  circuit 
remains  disconnected  from  the  coil  until  the  latter 
has  revolved  through  90°  and  again  approaches 
within  45°  of  its  next  position  of  maximum 
activity.  This  occurs  twice  during  each  revolu- 
tion of  every  coil.  That  is  to  say,  twice  during 
every  revolution  of  the  coil  it  is  open  and  con- 
tributes nothing  to  the  outside  circuit.  An  arma- 
ture wound  in  this  way  is  called  an  open  coil 
armature.  Such  construction  is  now  never  found 
upon  street  railway  apparatus  of  any  kind,  either 
motors  or  generators,  but  is  thought  to  have  some 
advantages  for  arc  lighting  dynamos,  and  is  the 
method  employed  on  both  the  Brush  and  Thom- 
son-Houston arc  dynamos. 

If,  instead  of  having  connected  the  coil  so  that 
it  was  out  of  circuit  except  when  generating  a 
certain  potential,  we  had  connected  it  so  that  it 


OPEN   AND    CLOSED   COIL   ARMATUBES.          101 

would  be  always  in  circuit  except  when  generating 
no  potential  at  all  (the  moment  of  reversal,  when 
it  would  be  short-circuited  by  the  brush),  we 
would  have  taken  advantage  of  the  small  electro- 
motive forces  which  we  threw  away  in  the  other 
arrangement  by  cutting  out  the  coils  before  they 
had  reached  and  after  they  had  passed  45*  of 
their  positions  of  maximum  activity. 

Fig.  35  shows  an  armature  wound  in  this  way.  By 
comparing  it  with  Figs.  32  and  33  (see  pages  93-4), 
it  will  be  seen  that  the  only  difference  between  the 
two  is  that  the  two  coils  are  really  the  one  a  con- 
tinuation of  the  other,  but  each  has  separate  con- 
nections with  its  own  commutator  segment.  Each 
coil  is  therefore  always  connected  with  the  out- 
side circuit — directly  through  its  commutator 
segments  when  the  latter  are  under  the  brushes, 
and  indirectly  through  the  other  coil  and  its  com- 
mutator blocks  when  its  own  have  passed  from 
beneath  the  brushes.  Armatures  thus  wound  are 
called  closed  coil  armatures,  and  are  the  kind  now 
universally  employed  both  for  generators  and 
motors  in  street  railway  equipments  and  for 
generators  in  incandescent  lighting  stations. 


CHAPTER  XI. 

DRUM   AND    RING     ARMATURES. 

BESIDES  the  two  classes  of  armatures,  open  and 
closed  coil,  above  outlined,  there  are  also  two  other 
classes  of  importance,  each  of  which  may  be  either 
open  or  closed  coil.  Reference  is  here  made  to 
what  are  termed  "  drum  "  and  "  ring  "  armatures. 
Those  heretofore  have  represented  the  wire  wound 
lengthwise  over  a  cylindrical  or  drum-shaped  core. 
They  are  therefore  for  this  reason  termed  "  drum  " 
armatures,  and,  as  before  stated,  may  be  either  open 
or  closed  coils. 

Instead  of  winding  our  wire  on  a  cylinder  we 
may  wind  it  on  an  iron  ring.  Fig.  36  represents 
an  elementary  open  coil  armature  of  this  kind  cor- 
responding to  the  open  coil  drum  armature  repre- 
sented in  Fig.  20  (see  page  78).  Another  form, 
with  two  coils,  is  shown  in  Fig.  37,  which  corre- 
sponds very  closely  with  the  drum  winding  in  Fig. 
31  (see  page  93).  Fig.  38  is  the  counterpart  in  the 
ring  type  of  armature  of  Fig.  32  (see  page  93),  in 
the  drum  winding. 

Fig.  39  (see  page  107)  shows  a  four-part  ring 
armature  of  the  closed  coil  type.  In  this  can  be 
shown  more  clearly  than  was  possible  in  the  drum 
armature  drawing  (Fig.  35,  see  page  99),  how  the 
various  coils  are  connected  together  and  to  the 
commutator  in  the  closed  coil  type  of  armature. 

Of  course  in  order  to  have  the  greatest  output 
102 


DRUM  AND   RING   ARMATURES.  103 

possible,  whether  the  armature  be  drum  or  ring 
winding,  open  or  closed  coil  type,  the  whole  of  the 
surface  of  the  core  is  overwound  with  wire,  and 
this  winding  is  divided  up  into  as  many  coils  as 
the  designer  desires,  the  two  ends  of  each  coil 
being  connected  to  appropriate  commutator  seg- 
ments, and  if  of  the  closed  coil  type  also  to  the  ends 
of  the  adjacent  coils.  In  the  closed  coil  ring  arma- 


FIG.  36. 

ture.  Fig.  40  (see  page  107),  shows  how  the  wind- 
ing is  really  one  continuous  coil  all  the  way  around 
the  ring,  its  two  ends  finally  being  joined  together. 
Then  the  number  of  turns  of  wire  that  shall  consti- 
tute a  coil  having  been  determined  on,  the  con- 
tinuous coil  is  tapped  at  those  intervals  and  con- 
nected by  means  of  a  short  piece  of  insulated 
copper  wire  with  a  commutator  bar  or  segment, 
as  is  also  shown  in  Fig.  40. 

Now  since  the  core  of  a  ring  armature  may  be 
regarded  as  a  cylinder,  just  like  that  used  in  the 
drum  armature,  with  its  center  cut  out,  it  is  evi- 
dent that  the  former  must  be  given  a  larger  diam- 
eter in  order  to  give  it  the  same  capacity  for  carry- 


104  ELECTKIC   KAIL  WAY   MOTORS. 

ing  lines  of  force,  and  the  latter,  instead  of  cutting 
directly  across  from  pole  to  pole  of  the  magnet  as 
they  do  in  the  drum  armature,  in  the  ring  armature 
follow  the  iron  in  preference  to  the  shorter  path 
through  the  air  space  in  the  center  (Fig.  41). 

The  fact  that  the  ring  armature  must  be  of 
larger  diameter  than  the  drum  armature  for  the 
same  capacity  prohibits  its  use  where  the  greatest 
power  is  required  in  the  smallest  possible  space, 
and  since  in  the  street  car  motor  this  is  a  first 
requisite,  we  seldom  see  the  ring  armature  em- 
ployed. On  the  other  hand,  in  machines  of  great 
size,  such  as  street  railway  generators,  it  is  more 
frequently  employed  than  the  drum  armature, 
chiefly  for  structural  reasons. 

CONSEQUENT   POLES    AND   MULTIPOLAB   FIELD 
MAGNETS. 

Heretofore  in  considering  magnets  we  have 
dealt  only  with  those  of  a  straight  bar  or  horse- 
shoe shape,  having  two  poles,  or  the  closed  iron 
ring,  with  the  closed  magnetic  circuit,  having  no 
poles  at  all.  Before  proceeding  further  it  may  be 
well  to  speak  of  two  other  forms  frequently  used 
both  in  dynamos  and  motors.  Suppose  we  have  a 
closed  magnetic  circuit,  as  in  Fig.  42,  and  place 
upon  it  on  one  side  a  coil  with  a  current  passing 
around  it  so  as  to  make  its  upper  portion  a  north 
pole  and  its  lower  portion  a  south  pole.  If  noth- 
ing more  were  done,  the  lines  of  force  would  flow 
around — part  of  them  through  the  armature,  and 
perhaps  a  greater  portion  would  flow  around 
through  the  other  leg  on  the  right.  All  these 
latter  would  be  lost,  so  far  as  our  armature  is  con- 
cerned. But  if  we  place  a  second  coil  on  the  leg 


CONSEQUENT   POLES. 


105 


so  as  to  make  the  upper  part  of  the  magnet  a  north 
pole  also,  it  will  drive  these  lines  back  and  send 
additional  lines  of  its  own  in  the  same  direction. 
In  fact,  the  effect  of  the  two  coils  working  in 
opposition  is  to  make  two  north  poles  adjoining 
each  other  above  and  two  south  poles  adjoining 
each  other  below,  as  shown  in  Fig.  42.  As  like 
poles  repel  each  other  their  lines  cannot  pass  each 
other,  but  are  forced  to  take  the  path  indicated. 


FIG.  37. 

When  the  direction  of  the  current  in  two  legs  of  a 
magnet  is  such  as  to  bring  two  poles  of  the  same 
kind  together,  the  latter  are  called  consequent 
poles. 

It  is  possible,  therefore,  in  any  piece  of  soft  iron, 
such  as  a  closed  ring,  for  instance,  by  dividing  the 
winding  up  into  any  number  of  coils,  and  passing 
the  current  through  adjacent  coils  in  opposite 
directions,  to  make  a  magnet  of  as  many  poles  as 
is  desired.  In  a  closed  ring,  or  equivalent  shape, 
with  a  single  coil,  if  there  be  no  leakage  of  lines 


106  ELECTRIC   RAILWAY   MOTORS. 

across  from  one  side  to  the  other,  there  will  be 
no  poles  at  all.  If  there  be  two  coils  upon  this 
ring  through  which  the  current  passes,  so  as  to 
compel  the.  lines  of  force  to  pass  around  in  oppo- 
site directions,  since  the  lines  induced  by  one  coil 
cannot  pass  through  the  other  coil,  the  lines  due 
to  both  coils  will  have  to  seek  another  path,  and 
will  emerge  from  the  ring  somewhere  between  the 
two  coils,  and  jumping  across  to  the  other  side 
along  the  path  offering  the  least  resistance,  re-enter 


FIG.  38. 

the   ring  again,   producing   consequent   poles,   as 
already  described  and  illustrated  in  Fig.  42. 

If  we  take  an  iron  ring  and  wind  it,  as  in  Fig.  43, 
with  four  coils,  A  B  G  D,  connecting  them  up  so 
that  the  current  will  travel  around  the  ring  in  the 
directions  indicated  by  the  arrows,  we  find  that 
the  directions  of  the  currents  in  coils  JB  and  (7,  if 
looked  at  from  a  point  in  the  ring  midway  between 
the  two,  will  be  in  the  opposite  direction  to  the 


CONSEQUENT   POLES. 


107 


travel  of  the  hands  of  a  clock.  Therefore  both 
currents  tend  to  make  the  space  between  them  a 
north  pole.  Moving  along  now  and  placing  our- 
selves in  the  ring  again  between  coils  A  and  J?, 


FIG.  39. 


FIG.  40. 


and  looking  towarcl  J?,  the  current  is  found  to  be 
flowing  around  the  ring  in  the  same  direction  as 
the  hands  of  a  clock.  That  end  of  the  coil  JB  at 
which  we  are  looking  is  therefore  a  south  pole. 


FIG.  41. 


Turning  around  and  looking  at  the  end  of  coil  A 
nearest  to  us,  we  find  that  the  current  as  we  see  it 
from  this  point  of  view  is  also  circling  around  in 
the  direction  of  the  hands  of  a  clock,  so  that  this 


108 


ELECTRIC    RAILWAY    MOTORS. 


end  of  J5  must  also  be  a  south  pole.  We  might 
have  known  this  without  looking  at  it,  for  if  the 
other  end  of  B  was  a  north  pole  this  end  must  be 
a  south  pole.  We  find  that  the  two  adjacent  ends 
of  the  coils  A  and  J3  are  south  poles,  so  the  space 
between  them  will  be  consequent  south  poles.  In 
like  manner  we  will  find  consequent  north  poles 
between  B  and  G  and  consequent  south  poles 


FIG.  42. 

between  C  and  D  as  lettered  in  the  diagram. 
Thus  we  have  a  magnet  with  four  poles — two 
south  poles  and  two  north  poles.  A  magnet  hav- 
ing but  two  poles,  such  as  described  in  the  earlier 
chapters  and  also  in  Fig.  42  (for  the  two  conse- 
quent poles  are  counted  as  one),  is  called  a  "bi- 
polar" magnet,  and  a  magnet  having  more  than 
two  poles,  as  shown  in  Fig.  43,  is  called  a  "  multi- 
polar  "  magnet. 


CHAPTER  XII. 

MULTIPLE    ABC    AND    SERIES    ARRANGEMENT. 

As  observed  in  Fig.  43  the  current,  before  it 
comes  to  the  magnet  coils,  divides — part  of  it  going 
through  coils  B  and  (7,  and  part  of  it  going  through 
A  and  D,  and  then  the  two  parts  unite  again  after 
having  passed  through  their  respective  coils.  It 
is  evident  that  instead  of  dividing  the  current  into 
two  circuits,  each  half  going  through  two  coils  in 
succession,  we  might  have  divided  it  into  four  cir- 
cuits, and  have  placed  each  coil  in  a  separate  circuit, 
or  we  need  not  have  divided  the  current  at  all, 
but  have  compelled  the  whole  of  our  current  to 
pass  through  first  A,  then  Dy  then  C  and  finally 
through  IB.  Fig.  44  represents  the  latter  arrange- 
ment. When  current  is  supplied  to  several  coils 
or  lamps  or  other  electrical  devices  or  groups  of 
the  same,  so  that  each  device  or  group  receives  a 
certain  fraction  of  the  whole  current  independently 
of  all  the  others,  viz.,  so  that  the  current  which 
passes  through  one  device  or  group  does  not  pass 
through  any  of  the  others,  as  would  be  the  case 
were  we  to  divide  our  circuit  into  four  in  one  of 
which  each  of  the  four  coils  are  placed,  these  four 
coils  would  be  said  to  be  in  " multiple  arc"  or  " in 
multiple"  with  each  other,  or  "in  parallel."  In 
Fig.  43  the  current  divides  between  two  circuits, 
the  current  of  one  of  these  circuits  passing  through 
the  group  of  coils  A  and  D,  and  the  current  of  the 


110 


ELECTRIC    RAILWAY    MOTORS. 


other  passing  through  the  group  -B  and  (7.1  These 
two  subordinate  circuits  are  therefore  in  multiple 
arc  with  each  other,  and  the  groups  of  coils  supplied 
by  each  circuit  are  said  to  be  "  in  multiple  arc  "  or 
"  in  parallel  "  with  each  other,  because  none  of  the 
current  which  passes  through  the  coils  A  and  D 
subsequently  passes  through  the  coils  B  and  C. 

If,  however,  the  current  reaches  its  translating 
devices  (the  term  "  translating  device  "  is  used  to 


FIG.  43. 

designate  anything  through  which  the  current 
passes  or  which  is  operated  by  the  current  either 
directly  or  indirectly)  not  at  the  same  time  or 
independently  as  in  previous  example,  but  passes 
through  them  in  succession,  so  that  the  same  cur- 


MULTIPLE    ABC.  Ill 

rent  which  passes  through  the  first  one  also  passes 
through  the  second  and  the  third  and  so  on  until 
all  are  thus  supplied,  the  various  devices  are  said 
to  be  "  in  series  "  with  one  another.  Thus  in  Fig. 
43,  while  coils  A  and  Z>,  considered  as  a  group,  are 
on  a  separate  circuit  from  B  and  (7,  and  the  cur- 
rent which  goes  through  A  and  D  does  not  after- 
ward pass  through  B  and  6T,  and  the  two  groups 
are  in  multiple  arc  with  each,  still,  if  we  regard  the 
coils  separately,  the  same  current  which  passes 
through  A  subsequently  passes  through  D,  and 
that  which  first  passes  through  B  also  passes 
through  C. 

A  and  D  are  therefore  in  series  with  each  other, 
and  B  and  G  are  likewise  in  series  with  each  other, 
but  if  we  arrange  our  coils  as  in  Fig.  44,  so  that 
the  same  current  which  passes  first  through  A 
and  then  through  D  also  passes  through  C  and  B 
in  the  order  named,  the  four  coils  are  then  said 
to  be  in  series  with  one  another.  If  the  circuit 
divides  before  it  comes  to  A,  one  branch  going 
around  the  four  coils,  as  just  described,  and  the 
other  branch  supplying  in  similar  manner  the 
coils  of  another  field  magnet,  then  the  two  groups 
of  field  magnets  will  be  in  parallel  with  each 
other,  while  the  various  coils  in  each  group  are 
in  series  with  the  others  of  the  same  group.  This 
is  exactly  a  similar  case  to  that  represented  in 
Fig.  43,  where  the  group  of  coils  A  and  -D,  while 
its  constituents,  A  and  D,  are  in  series  with  each 
other,  is  in  multiple  arc  or  in  parallel  with  the 
other  group  of  coils,  B  and  C,  whose  constituents, 
B  and  C,  are  in  series  with  each  other. 

Such  an  arrangement  as  this,  where  the  trans- 
lating devices  are  divided  up  into  groups,  the 
members  of  each  group  forming  a  series,  but  the 


112 


ELECTRIC    RAILWAY    MOTORS. 


various  groups  being  in  multiple  arc  with  each 
other,  is  called  a  "  multiple  series  "  arrangement. 

If  in  Fig.  44*  the  current,  after  having  passed 
through  all  four  coils,  is  carried  to  another  group 
of  magnets  or  coils,  these  two  larger  groups  will 
be  in  series  with  one  another. 

Figs.  45,  46  and  47  represent  respectively  the 
series,  the  multiple  arc  and  multiple  series  ar- 
rangement for  translating  devices.  There  is  also 


FIG 


a  fourth  arrangement,  represented  in  Fig.  48, 
which  is  sometimes  called  the  "  series  multiple  " 
arrangement. 

It  is  well  to  fix  thoroughly  in  mind  the  charac- 
teristics of  the  series,  multiple  arc  and  multiple 
series  arrangements,  as  they  will  be  frequently  re- 
ferred to  hereafter,  and  a  thorough  understanding 
of  them  is  essential  to  an  intelligent  reading  of 
what  follows.  To  facilitate  this  understanding  it 


GENERATORS.  113 

may  assist  us  if  we  remember  that  the  incandes- 
cent lamps  in  a  street  car  are  arranged  five  in 
series.  The  street  cars  themselves  are  in  multiple 
arc  with  each  other,  as  are  also  the  generators  at 
the  power  house  if  there  be  more  than  one  con- 
nected to  the  same  feeder.  Most  of  the  incandes- 
cent lamps  except  those  in  street  cars  are  arranged 
in  multiple  arc,  whereas  almost  all  the  arc  lamps 
used  for  street  lighting  are  arranged  in  series. 


FIG.  45. 

The  motors  under  the  cars  are  connected  up  in 
various  ways  according  to  the  position  of  the  con- 
trolling switch  and  the  system  of  equipment  em- 
ployed ;  sometimes  the  two  motors  are  in  multiple 
arc  with  each  other,  and  sometimes  they  are  in 
series,  and  the  coils  of  their  field  magnets  are 
thrown  into  various  combinations  of  series,  mul- 
tiple series  and  multiple  arc,  each  arrangement 
being  employed  for  some  specific  purpose. 

CURRENT   CHARACTERISTICS    OF   MULTIPLE  AND 
SERIES   ARRANGEMENTS    IN    GENERATORS. 

If  two  pumps  standing  side  by  side  pump  water 
into  the  same  main,  they  will  not  increase  the 
pressure  of  the  water,  but  will  increase  the  amount 
of  water  only.  So  if  two  dynamos  are  connected 
in  parallel  or  multiple  arc  with  the  same  trolley 
or  feeder  wire,  the  potential  of  the  resulting  cur- 
rent will  not  be  increased,  but  the  number  of 


114  ELECTRIC  RAILWAY  MOTORS. 

amperes  which  may  be  drawn  from  that  circuit, 
or  the  number  of  car's  or  lights  or  other  translat- 
ing devices  that  may  be  supplied,  will  be  equal  to 
the  sum  of  those  that  could  be  supplied  by  both 
separately. 

If,  however,  one  of  two  pumps  delivers  to  the 
other  so  many  gallons  of  water  per  minute  at  a 
pressure  of  say  100  pounds  per  square  inch,  and 


FIG.  46. 


the  second  pump  receives  that  water  into  its 
cylinders  at  that  pressure  and  passes  it  on  to  the 
main  with  an  additional  pressure  of  say  50  pounds 
per  square  inch,  the  amount  of  water  pumped 
into  the  main  will  not  be  increased  by  reason  of 
the  second  pump,  but  its  pressure  will  have  been 


FIG.  47. 

increased  so  as  to  equal  the  sum  of  the  pressures 
imparted  by  both  pumps,  in  this  case  equal  to  150 
pounds  per  square  inch. 

So  if  one  dynamo  pumps  current  into  another 
which  passes  it  on  to  the  line  wire,  or,  in  other 
words,  if  two  dynamos  are  connected  in.  series, 
the  number  of  amperes  that  can  be  drawn  from 
that  circuit  will  not  be  greater  than  if  but  one 
machine  were  working,  but  it  will  be  at  a  pressure 


GENERATORS.  115 

equal  to  the  sum  of  the  pressures  impressed  upon 
the  current  by  both. 

If  in  our  power  house  we  have  a  500-volt 
dynamo  capable  of  furnishing  sufficient  current 
to  operate  ten  cars,  and  it  becomes  necessary  to 
double  our  equipment  of  cars,  we  would  put  in 
another  500-volt  dynamo  of  the  same  capacity  and 
connect  it  up  in  multiple  with  the  first  one,  and 
the  question  is  solved. 

If,  on  the  other  hand,  we  had  a  100-volt  incan- 
descent lighting  dynamo,  and  wished  to  supply  a 
500-volt  circuit  for  street  car  purposes,  we  would 
have  to  connect  up  others  in  series  with  it  whose 
potentials  were  such  that  when  added  together 
and  to  that  of  the  machine  already  installed  they 


FIG.  48. 

would  equal  500.  Thus  we  might  add  4  more 
machines  of  100  volts  each,  making  5  machines 
in  series  whose  combined  electromotive  forces 
would  be  500,  or  2  machines  of  200  volts  each, 
or  1  machine  of  100  volts  and  another  of  300 
volts.  But  if  the  original  machine  only  had  a 
capacity  of  say  100  amperes,  the  5  connected  in 
series  would  have  no  greater  output. 

The  rule,  therefore,  may  be  laid  down  that  a 
combination  of  generators  in  multiple  arc  gives 
an  output  in  amperes  equal  to  the  combined  out- 
put of  the  several  machines,  but  with  no  increase 
in  pressure,  while  a  combination  of  generators  in 
series  gives  a  pressure  equal  to  the  combined 
pressures  of  the  several  machines,  but  with  no  in- 
crease in  amperes. 


CHAPTER  XIII. 

CURRENT     CHARACTERISTICS     IN    TRANSLATING 
DEVICES. 

WHEN  there  are  no  cars  on  the  line,  or  the 
trolley  wire  is  not  otherwise  connected  with  the 
rails  or  the  ground,  the  resistance  between  the  two 
is  infinitely  great,  and  no  current  will  pass  from 
one  to  the  other.  If  one  car  be  now  put  into 
operation,  one  path  will  be  opened  to  the  current 
from  the  trolley  wire  to  the  rails.  If  now  a 
second  car  and  a  third  be  placed  in  operation,  a 
second  and  a  third  path  will  be  opened,  and  if  the 
resistances  of  all  three  of  these  paths  be  the  same 
the  resistance  between  the  trolley  wire  and  the 
rail  when  two  cars  are  in  operation  will  only  be 
one-half,  and  when  three  cars  are  going  one-third 
what  it  was  when  but  one  car  was  receiving  cur- 
rent ;  the  pressure  will  remain  the  same  with  the 
addition  of  cars  in  multiple  ;  but  as  each  car  put 
into  service  opens  a  new  path  for  the  current 
between  the  trolley  wire  and  the  rail,  the  number 
of  amperes  of  current  that  will  flow  will  increase 
with  the  number  of  cars — will  be  twice  as  much 
for  two  and  three  times  as  much  for  three  cars  as 
for  one. 

A  parallel"  case  is  found  in  the  consumption  of 
water.  Supposing  we  have  a  line  of  water  mains 
connected  with  a  reservoir  500  feet  high.  The 
pressure  of  water  in  the  mains  at  their  lowest 

116 


TRANSLATING   DEVICES.  11 7 

point  would  be  that  due  to  500  feet  of  head. 
Now  suppose  we  have  a  number  of  small  faucets 
tapped  into  the  main  at  its  lowest  point.  When 
they  are  all  turned  off,  the  strength  of  the  main, 
or  its  resistance,  while  not  infinitely  great,  as 
in  the  illustration  of  the  trolley  wire,  is  still  suffi- 
ciently great  so  that  no  water  can  flow  out  at  any 
point.  Open  one  faucet  and  a  single  path  of,  we 
will  say,  unknown  resistance  is  opened,  and  a 
stream  of  so  many  quarts  or  gallons  per  minute 
will  flow  out  onto  the  ground.  Open  a  second 
faucet  and  another  path  of  equal  resistance  will  be 
opened,  and  double  the  quantity  of  water  will  flow. 
The  same  quantity  would  flow  if,  instead  of  open- 
ing a  second  faucet  of  the  same  resistance  as  the 
other,  the  first  one  were  closed  and  another  one  of 
double  the  capacity  or  offering  half  the  resist- 
ance were  turned  on  in  its  stead.  Therefore, 
while  by  opening  one  small  faucet  we  have 
decreased  the  resistance  of  the  pipe  from  some- 
thing more  than  sufficient  to  keep  back  water 
under  500  feet  pressure  to  some  definite  quantity 
which  is  less  than  that,  by  opening  two  of  the 
same  size  we  have  divided  the  resistance  remain- 
ing by  two,  and  by  turning  on  a  third  it  will  be 
reduced  to  one-third  what  it  was  when  but  one 
was  turned  on.  But  no  matter  how  many  faucets 
we  open,  nor  how  much  water  runs  out  (provided, 
of  course,  it  does  not  exceed  the  capacity  of  the 
main  or  the  reservoir  is  not  emptied),  our  reservoir 
remains  500  feet  above  us,  and  the  pressure  will 
remain  the  same  at  the  faucets. 

We;may  make  the  resemblance  between  the 
electric  flow  and  the  flow  of  water  still  more 
striking  by  supposing  that  each  faucet  connects 
with  a  little  water  motor  which,  when  working  to 


118  ELECTEIC    BAIL  WAY    MOTORS. 

its  fullest  capacity,  requires  a  stream  of  water  as 
large  as  that  which  can  run  out  of  the  faucet  when 
turned  on  full  under  500  feet  head. 

13y  turning  on  the  faucet  part  way,  with  500 
feet  head  of  water  behind  it,  enough  water  will 
flow  to  enable  the  motor  to  do  a  fraction  of  its 
maximum  work,  turn  it  further  it  will  do  more, 
and  finally  turn  it  on  full  and  it  will  do  the  most 
that  it  is  capable  of  doing.  A  second  and  a 
third  water  motor  may  be  attached  to  other  similar 
faucets  and  be  caused  to  do  varying  amounts  of 
work  by  turning  on  more  and  more  water,  but 
whether  the  motors  are  doing  little  or  much  work, 
using  little  or  much  water,  the  pressure  in  the 
main  will  not  decrease  until  so  many  motors  are 
attached  as  to  require  for  their  operation  more 
water  than  the  main  can  carry.  If  the  capacity 
of  the  main  be  exceeded,  it  will  be  necessary  to 
lay  a  larger  main,  and  if  this  be  fed  by  two  pipes 
of  the  same  size — the  original  pipe  from  the  same 
reservoir  and  another  one  from  another  reservoir 
at  the  same  height — the  pressure  on  the  main  will 
not  be  increased,  but  its  capacity  for  running 
water  motors  will  be  doubled. 

While  there  will  have  been  no  water  consumed 
by  the  water  motors,  for  the  reason  that  just  as 
many  gallons  will  flow  away  from  the  motor  as 
was  delivered  to  it,  that  which  flows  away  has 
lost  its  pressure.  If,  for  example,  it  required  just 
10  gallons  per  minute  under  450  feet  of  pressure 
to  drive  each  vinotor  at  its  fullest  capacity,  and 
the  motor  received  that  amount  of  water  at  500 
feet  pressure,  it  may  be  said  to  absorb  the  pressure 
due  to  450  feet,  and  the  water  will  flow  away 
from  the  wheel  at  the  rate  of  10  gallons  per 
minute,  but  having  a  head  of  but  50  feet.  That 


TRANSLATING   DEVICES.  119 

is  to  say,  a  pressure  equivalent  to  that  exerted 
by  a  column  of  water  450  feet  high  will  have  dis- 
appeared in  operating  the  water  wheel.  A  second 
wheel  requiring  a  pressure  of  450  feet  head  placed 
below  the  first  wheel  could  not  be  operated,  be- 
cause the  remaining  head  would  not  be  sufficient, 
and  if  the  two  were  placed  together  in  this  man- 
ner— in  series — neither  of  them  could  be  operated 
to  their  full  capacity,  because  when  thus  placed 
their  combined  resistances  would  be  opposed  to  the 
water — that  is  to  say,  the  resistance  of  both  would 
be  double  that  of  one,  and  the  amount  of  water 
that  would  pass  through  either  would  be  only  half 
as  much  as  when  there  was  but  one.  If  we  increase 
our  pressure, however,  more  water  will  flow  through 
our  faucet  and  from  one  motor  to  the  other,  until 
when  we  have  doubled  our  pressure,  or  connected 
our  main  to  a  reservoir  900  feet  high,  both  motors 
will  be  operated  at  their  maximum  capacity. 
The  water  running  away  from  our  last  motor  will 
then  have  no  pressure,  each  motor  having  ab- 
sorbed a  head  of  450  feet  ;  the  same  amount  of 
water,  10  gallons  per  minute,  will,  however,  be 
found  to  have  passed  through,  but  it  is  no  longer 
capable  of  doing  any  work. 

Thus  we  see  that  by  operating  translating  de- 
vices in  series  we  consume  pressure  (volts),  and 
not  current  (amperes),  which  is  just  the  reverse  of 
what  takes  place  in  the  generating  station  where 
we  connect  generators  in  series,  thereby  increas- 
ing the  volts  with  the  number  of  machines,  but 
gaining  nothing  in  the  way  of  amperes. 

Take  the  case  of  an  incandescent  dynamo  giving 
current  at  about  100  volts.  Each  16  C.  P.  lamp 
requires  when  working  at  its  normal  rate  about 
J  ampere  of  current  at  100  volts.  That  is  to 


120  ELECTEIC    RAILWAY    MOTOES. 

say,  its  resistance  is  such  that  it  requires  a  pres- 
sure of  about  100  volts  to  force  sufficient  current 
through  the  filament  to  heat  the  latter  to  a 
white  heat.  If  our  dynamo  had  a  maximum  ca- 
pacity of  100  amperes  at  100  volts,  and  our  lamps 
required  £  ampere  each,  200  lamps  could  be  fully 
supplied  by  the  circuit  if  placed  in  multiple  arc  with 
one  another,  because  there  would  be  enough  cur- 
rent to  go  round  and  it  would  be  delivered  to  each 
lamp  under  the  same  pressure.  Its  capacity,  how- 
ever, would  then  be  exhausted.  If  we  connect  up  a 
second  dynamo  of  equal  capacity  to  the  same  cir- 
cuit in  multiple  arc  with  the  other,  200  additional 
lamps  could  be  supplied  in  the  same  way.  But 
supposing  we  place  2  lamps  in  series  across  the 
circuit :  their  resistances  would  be  added,  and  at  100 
volts  pressure  but  half  as  much  current  could  flow, 
viz.,  j-  ampere.  The  lamps,  we  have  stated,  re- 
quired J-  ampere  each,  hence  if  2  were  placed  in 
series  neither  would  be  heated  sufficiently  to  give 
much  light.  If,  however,  we  connect  our  dynamos 
in  series  so  as  to  double  the  electromotive  force  or 
pressure  of  the  circuit,  the  required  quantity,  % 
ampere,  would  be  forced  through  the  combined 
resistance  of  the  2  lamps,  and  both  would  burn  at 
their  normal  candle  power.  A  single  lamp,  unless 
of  double  the  resistance  of  those  heretofore  used, 
could  not  be  used  on  this  200-volt  circuit,  as  the 
pressure  would  be  so  great  as  to  immediately 
break  it.  For  the  same  reason  we  cannot  put 
100-volt  lamps  in  our  cars  in  multiple  arc  arrange- 
ment, for  they  would  all  be  destroyed  by  the  500- 
volt  pressure,  as  fast  as  they  could  be  placed  in 
their  sockets.  But  if  each  lamp  absorbs  100  volt 
of  pressure,  and  each  added  to  a  series  consumes 
the  same  number  of  volts,  if  we  place  5  lamps 


MULTIPOLAR 


OF  THE 

UNIVERSITY 

OF 

121 


in  series  on  the  usual  500-volt  circuit,  there  will 
be  just  enougli  pressure  to  give  each  of  them  what 
is  required  to  operate  it  at  normal  candle  power. 
We  are  thus  limited  on  street  cars  operating  on 
the  usual  500-volt  circuits  to  5  lamps  placed  in 
series.  If  we  want  more,  we  must  arrange  another 
series  of  5,  for  if  we  placed  6  or  7  on  the 
first  series  each  would  only  receive  -fa  or  \  of  500 
volts,  which  would  not  be  sufficient  to  illuminate 
them  to  full  candle  power,  and  if  we  placed  but  1 
or  2  on  the  second  circuit,  in  the  case  of  the 
single  lamp  it  would  receive  the  full  pressure  of 
500  volts,  and  in  the  case  of  2  lamps,  each  would 
receive  250  volts,  which  in  both  cases  would  be 
entirely  too  much.  We  might,  of  course,  make  up 
the  second  series  of  1  or  2  lamps  and  dead 
resistances  equivalent  to  the  resistance  that  would 
be  offered  by  the  additional  lamps  required  to 
make  up  the  series  of  5,  but  these  dead  resist- 
ances would  consume  as  much  energy  as  the  lamps 
they  replaced  and  give  no  useful  return,  so  that  it 
would  be  much  better  to  complete  the  second  series 
with  lamps  than  with  dead  resistances.  If  we  had 
a  second  series  of  5  lamps,  this  second  series  would 
be  in  multiple  with  the  first. 

The  same  reason  which  compels  us  when  using 
100-volt  lamps  on  a  500-volt  circuit  to  place  5  of 
them  in  series  would  compel  us  in  case  our  circuit 
was  at  1000  volts  to  use  10  lamps  in  series. 

MTJLTIPOLAE    FIELDS. 

Referring  to  Fig.  43  we  see  how  an  unbroken 
iron  ring  may  be  wound  so  as  to  have  four  distinct 
poles.  In  practice  it  is  desirable  to  have  as  lit- 
tle air  space,  bet  ween  these  polar  surfaces  and  the 
armature  as  possible,  and  for  this  purpose  the  ring 


122  ELECTRIC   RAILWAY   MOTORS. 

which  is  to  become  our  multipolar  magnet  is  cast 
with  extensions,  called  pole  pieces,  extending  in- 
wardly, and  the  magnetizing  coils  are  wound  upon 
these  extensions.  Fig.  49  (see  page  124)  shows  this 
arrangement  for  a  four-pole  field,  also  the  direc- 
tions taken  by  the  lines  of  force.  It  is  clear  that  in 
a  four-pole  magnet  we  have  tile  exact  equivalent 
of  two  simple  magnets,  and  a  wire  on  the  surface 
of  an  armature  revolving  in  this  field  will  pass 
four  poles  in  one  revolution.  As  it  sweeps  by  the 
first  north  pole  it  will  generate  a  maximum  elec- 
tromotive force  in  a  given  direction.  This  will 
decrease  until  it  gets  halfway  between  the 
north  and  south  poles,  where  it  will  become  zero 
and  change  its  direction.  That  is,  it  will  come  to 
the  point  where  the  currents  must  be  commu- 
tated  in  order  to  maintain  them  in  the  same  di- 
rection. From  this  point  until  it  passes  the  adja- 
cent south  pole  the  generated  electromotive  force 
will  be  increasing.  It  then  decreases  until  it  is 
zero  at  a  position  halfway  be  ween  the  south  pole 
and  the  next  north  pole,  where  it  must  be  commu- 
tated  again,  and  so  on  until  the  armature  has  made 
a  complete  revolution.  Thus  in  a  four-pole  field 
the  currents  in  the  armature  wires  in  every  revo- 
lution reach  a  maximum  four  times  instead  of 
twice,  as  in  the  two-pole  field — once  every  time 
they  pass  a  polar  surface;  they  also  become  zero 
and  change  their  direction  four  times — midway 
between  the  poles  ;  and,  if  the  currents  are  to  be 
maintained  continuous^  in  the  same  directions, 
they  must  be  commutated  whenever  these  changes 
of  direction  occur.  There  will,  therefore,  be 
required  four  brushes  in  this  case  instead  of  two. 
In  a  six-pole  field  there  will  be  six  reversals  and 
there  must  be  six  brushes,  and  so  on;  two  additional 


MULTIPOLAR   FIELDS.  123 

brushes  must  be  added  for  every  additional  pair 
of  poles  introduced  into  our  field.  In  Fig.  50  is 
shown  the  arrangement  of  the  brushes  in  a  four- 
pole  machine,  the  ring  winding  being  used  for 
illustration  as  being  simpler  for  the  purpose.  In 
the  bipolar  (two  pole)  field  it  will  be  remembered 
that  the  positive  brush  was  placed  diametrically 
opposite  the  negative  brush.  In  the  four-pole 
field  this  is  not  so,  because  the  north  pole  of  the 
magnet  is  not  opposite  the  south  pole.  They  are 
at  right  angles  to  each  other,  and  therefore  in 
order  that  the  brushes  may  have  the  same  posi- 
tion relative  to  the  field  that  they  had  before,  viz., 
at  right  angles  to  them,  they  are  in  the  four-pole 
field  at  right  angles  to  each  other  also.  It  will  be 
seen  from  Fig.  50  tfyat  the  positive  and  negative 
brushes  alternate,  #nd  by  connecting  two  circuits 
in  the  proper  way  to  these  brushes  we  would  have 
two  independent  currents.  In  fact,  while  in  the 
four-pole  field  we  have  practically  two  separate 
bipolar  magnets,  we  also  have,  when  a  single 
armature  is  added,  practically  two  distinct  gener- 
ators or  motors.  Or,  as  is  more  usually  the  case, 
these  two  independent  circuits  are  united  into  one, 
and  we  have,  if  everything  is  properly  arranged 
and  proportioned,  a  single  machine  equivalent 
to  the  output  of  the  two  considered  separately. 
It  is  evident-that  this  can  be  accomplished  by  con- 
necting the  two  positive  brushes  (those  marked  -|-) 
together  and  to  one  end  of  the  circuit,  and  the  two 
negative  brushes  (those  marked — )  to  the  other  end 
of  the  circuit,  and  in  large  multipolar  generators 
this  is  usually  the  method  employed,  all  of  the 
brushes  from  which  the  current  is  coming  (the  posi- 
tive brushes),  being  connected  together  and  all  of 
those  into  which  the  current  is  passing  (the  nega- 


124 


ELECTRIC    RAILWAY    MOTORS. 


tive  brushes)  being  connected  together,  and  these 
are  attached  to  the  positive  and  negative  terminals 
of  the  line  circuit. 

When  the  brushes  of  the  same  kind  are  thus 
connected  together,  the  electromotive  force  of  the 
whole  armature  is  simply  that  of  any  of  the  sets 
of  coils  from  one  positive  brush  to  the  adjacent 
negative  brush.  In  the  diagram  (Fig.  50),  see  page 
126,  the  coils  of  the  four  quarters  of  the  armature 
are  in  multiple  arc  with  each  other,  and  since  there 


FIG.  49. 

are  therefore  four  paths  of  the  same  size  for  the 
current,  the  resistance  oifered  to  the  passage  of  the 
current  is  only  one-fourth  what  it  would  be  if  the 
coils  of  all  four  were  in  series,  or  if  the  coils  on 
one-half  the  armature  were  in  parallel  with  those 
on  the  other  half,  as  would  be  the  case  were  this  a 
bipolar  field  and  there  were  but  two  brushes. 

Referring  again  to  Fig.  50,  since  in  a  four- pole 
field  the  opposite  poles  are  alike,  the  coils  on  the 
armature,  diametrically  opposite  to  each  other  as 
they  sweep  by  these  poles,  will  always  have  elec- 


MULTIPOLAK    FIELDS.  125 

tromotive  forces  generated  in  them  in  the  same 
direction.  This  being  the  case,  we  can  connect 
the  diametrically  opposite  coils  with  each  other, 
either  in  series  or  in  multiple,  so  that  they  prac- 
tically form  but  one  coil,  and  by  bringing  the 
ends  of  this  coil  to  the  proper  commutator  blocks, 
again  reduce  the  number  of  brushes  to  two.  In 
this  case  the  brushes  will  be  most  conveniently 
located  at  right  angles  to  each  other,  about  half- 
way between  a  north  pole  and  its  two  adjacent 
south  poles,  or  between  a  south  pole  and  its  two 
adjacent  north  poles.  It  is  evident  that  if  oppo- 
site coils  be  connected  in  series  the  electro- 
motive force  generated  will  be  doubled,  while  the 
resistance  is  also  doubled,  and  if  they  are  con- 
nected in  parallel  the  electromotive  force  will  be 
that  of  either  coil  alone,  while  the  current  will  be 
doubled  and  the  resistance  halved.  This  method 
of  connecting  together  the  opposite  coils  of  an 
armature  in  a  multipolar  field  is  the  usual  one  in 
multipolar  street  car  motors,  for  the  reason  that 
it  reduces  the  number  of  brushes,  which  is  a  very 
desirable  accomplishment,  and  also  enables  the 
brashes  to  be  more  conveniently  located  for  in- 
spection than  would  otherwise  be  possible. 

We  will  have  noticed  another  advantage  in  mul- 
tipolar machines.  In  discussing  bipolar  machines 
it  was  stated  that  in  any  given  case  the  electro- 
motive force  generated  by  a  coil  revolving  in  a 
magnetic  field  depended  upon  the  number  of  revo- 
lutions it  made  per  minute  in  that  field,  or,  in  other 
words,  upon  the  rapidity  with  which  it  cut  the 
lines  of  force.  We  have  just  seen  that  in  a  four- 
pole  field  the  coil  cuts  the  lines  of  force  twice  as 
often  in  each  revolution  as  it  does  in  a  bipolar  field. 
The  armature,  therefore,  need  revolve  only  half 


126 


ELECTEIC    RAILWAY    MOTOBS. 


as  fast  in  a  four-pole  field  as  in  one  of  two  poles 
to  produce  the  same  output,  and  thus  we  are 
enabled  to  make  slow-speed  generators.  The 
same  may  be  said  of  motors,  and  it  will  have  been 
observed  that  all  slow-speed  motors,  such  as  the 
gearless  motors,  are  provided  with  multipolar 
fields.  The  philosophy  of  this,  simply  stated,  is 
that  if  a  given  current  fed  to  a  motor  having  two 


FIG.  50. 

poles  will  give  it  at  any  specified  speed  a  given 
power,  the  same  current  acting  upon  a  motor  with 
four  poles  would  produce  a  motor  practically 
equivalent  to  two  machines  of  the  bipolar  type, 
and  as  the  power  of  a  motor  is  also  dependent 
upon  its  speed,  a  four-pole  motor  will  produce  the 


MULTIPOLAR    FIELDS.  127 

same  power  at  half  the  speed  of  a  similar  motor 
with  only  two  poles. 

Thus  far  we  have  said  nothing  as  to  how  we  get 
the  magnetism  in  our  field  magnets.  We  have 
assumed,  however,  that  they  are  electromagnets, 
viz.,  that  the  field  magnets  are  made  of  soft  iron 
and  have  no  magnetism  of  their  own,  but  are  con- 
verted into  magnets  by  passing  electric  currents 
through  coils  of  insulated  wire  properly  wound 
around  them,  and  this  is  now  the  universal  prac- 
tice in  all  but  very  small  generators.  Permanent 
magnets  made  of  very  hard  tempered  steel  might 
be  used,  however,  but  as  a.  permanent  magnet  can 
never  be  made  so  strong  as  an  electromagnet  of 
the  same  size,  and  for  other  equally  good  reasons 
which  need  not  be  mentioned  here,  the  latter  are 
preferred.  The  earlier  dynamos  were,  however, 
frequently  constructed  with  permanent  magnets. 
Such  machines  are  properly  called  magnetoelectric 
machines.  Examples  of  magnetoelectric  ma- 
chines are  found  in  the  apparatus  employed  in  the 
telephone  fixtures  for"  ringing  up  the  exchange. 
In  the  call  box  will  be  found  a  strong  permanent 
magnet  between  whose  poles  there  revolves  a  small 
iron  bobbin  (armature)  wound  with  fine  wire.  As 
this  is  rotated  by  turning  the  crank  it  generates 
alternating  currents  which  pass  over  the  line  and 
ring  the  bells.  It  would  be  a  simple  thing  to  attach 
a  commutator  to  the  armature  which  would  con- 
vert the  alternating  currents  into  direct  currents, 
as  already  described,  but  the  telephone  call  bell  has 
been  adapted  to  alternating  currents,  so  that  the 
complication  of  commutators  is  not  necessary. 

Another  method  of  obtaining  our  magnetism  is 
to  construct  our  fields  of  soft  iron  and  wind  them 
with  coils,  and  connect  these  coils  with  some  inde- 


128  ELECTRIC    RAILWAY    MOTORS. 

pendent  source  of  electricity,  such  as  a  large  bat- 
tery or  another  dynamo.  When  the  current  flows 
through  the  coils,  of  course  the  fields  become 
highly  magnetized,  as  we  have  seen.  A  machine 
whose  fields  are  thus  excited  is  called  a  separately 
excited  dynamo.  This  method  has  some  advantages, 
chief  of  which  is  that  the  exciting  current,  coming 
from  a  separate  source,  is  entirely  independent  of 
the  fluctuations  of  current  in  the  trolley  circuit, 
which  would,  if  current  from  the  latter  were 
added,  produce  similar  variations  in  the  magnet- 
ism of  the  fields,  which  would  in  turn  still  further 
complicate  matters.  It  has  the  disadvantage,  how- 
ever, of  requiring  a  separate  machine  for  this  pur- 
pose, which  in. very  small  plants  would  be  scarcely 
warranted  by  the  attendant  advantages.  In  large 
electric  power  stations  it  is  quite  customary  to  find 
a  small  machine  used  solely  for  this  purpose,  its 
current  being  employed  to  excite  the  fields  of  all 
generators  in  the  plant. 


CHAPTER  XIV. 

THE   DYNAMO-ELECTRIC    PRINCIPLE. 

THERE  is  still  a  third  method,  and  this  is  the 
most  usual  one,  viz.,  to  make  the  dynamo  excite 
its  own  fields  by  causing  either  all  or  a  portion  of 
the  current  generated  by  the  armature  to  pass 
around  the  field  magnet  coils.  But  the  question 
naturally  arises,  how  are  we  to  start  such  a  ma- 
chine into  action  ?  When  the  armature  stops,  the 
current  stops,  and  the  magnetism  of  the  fields 
disappears.  If  we  start  the  machine  from  rest, 
there  being  no  magnetism  in  the  fields,  there  will 
be  no  lines  of  force  for  the  armature  wires  to  cut; 
the  armature  will  therefore  generate  no  current, 
and  our  provision  for  utilizing  that  current  to 
excite  our  field  will  be  useless.  So  reasoned  the 
early  builders  of  electrical  machines,  and  it  was 
thought  necessary  for  a  long  time  to  separately 
excite  the  fields,  at  least  until  the  machine  got  into 
action.  It  was  therefore  a  very  important  dis- 
covery that  such  was  not  necessary.  It  seems  that 
all  iron,  however  soft,  has  a  little  magnetism,  which 
it  either  derives  from  the  earth's  magnetism 
or  retains  from  previous  magnetization  (residual 
magnetism). 

This  may  be  very  slight,  but  it  is  suflicient  so 
that  when  the  armature  is  revolved  before  the 
pole  pieces  it  generates  a  very  slight  current.  No 
matter  how  insignificant  this  current  may  be,  as  it 


130  ELECTRIC    RAILWAY    MOTORS. 

passes  around  the  field  magnets  it  adds  somewhat 
to  their  magnetism.  This  increased  magnetism 
of  the  fields  enables  the  armature  to  generate  a 
little  stronger  current  than  before,  and  this  pro- 
duces more  magnetism  and  that  more  current,  so 
that  by  the  continued  reaction  between  the  field 
and  armature  the  machine  "builds  itself  up,"  as 
the  phrase  is,  until  the  magnets  have  arrived  at 
full  strength,  and  the  armature  is  putting  out 
current  to  its  maximum  capacity. 

This  "  building  up  "  of  the  machine  from  prac- 
tically nothing  to  its  maximum  output  without 
outside  help  except  from  the  power  necessary  to 
drive  the  armature,  seeming  at  first  sight  to  be  very 
much  like  the  attempt  to  lift  one's  self  over  the 
fence  by  one's  boot  straps,  is  known  as  the  "  dy- 
namo-electric" principle.  These  "  self  -exciting  " 
machines,  which  are  by  far  the  most  numerous  of 
those  emploj^ed  to-day,  are  the  true  "  dynamo- 
electric  "  machines. 

SERIES,    SHUNT   AND    COMPOUND  WINDING. 

The  dynamo-electric  principle  gives  rise  to  three 
distinct  types  of  machines.  In  the  first  type  all  of 
the  current  from  the  armature  passes  around  the 
field  coils,  as  in  Fig.  51,  before  it  goes  out  to  the 
exterior  circuit.  Since  the  field  coils  are  in  series 
with  the  armature,  a  machine  so  wound  is  called  a 
series  dynamo  or  motor,  as  the  case  may  be.  It  is 
evident  that  if  resistances  are  placed  in  the  outer 
circuit  the  amount  of  current  that  will  flow  around 
the  coils  will  be  lessened.  This  will  lessen  the 
strength  of  the  field  magnets,  and  this  will  still 
further  lessen  the  amount  of  current  that  the 
armature  can  give  ;  and  if  the  exterior  circuit 


SERIES,  SHUNT  AND  COMPOUND  WINDING.      131 

becomes  broken  so  that  no  current  can  flow,  of 
course  the  field  magnets,  no  longer  having  any 
current  in  their  coils,  lose  their  magnetism,  and  the 
armature  ceases  entirely  to  generate  current.  If 
the  break  in  the  outer  circuit  be  now  closed  again, 
the  dynamo  will  gradually  build  itself  up,  as  before 
described  under  the  heading  "Dynamo-Electric 
Principle,"  until  it  again  attains  its  full  strength, 
but  this  will  take  an  appreciable  time.  A  series 
dynamo,  of  course,  could  not  be  used  on  a  multiple 


arc  street  railway  or  on  the  usual  incandescent 
circuit,  for  on  either  of  these  circuits  we  want  to 
have  at  our  command  the  full  strength  of  the  cur- 
rent the  moment  we  start  the  first  car  or  turn  on 
the  first  light.  We  cannot  wait  for  the  dynamos 
to  build  themselves  up.  There  are  other  objec- 
tions also  to  series  dynamos  for  these  purposes,  but 
for  other  purposes  they  have  their  use. 

In  the  second  type  (Fig.  52)  we  only  use  a  por- 
tion   of  the  current  generated  by  the  dynamos  to 


132 


ELECTRIC    RAILWAY    MOTORS. 


excite  the  fields.  From  the  brushes  there  are  two 
circuits,  between  which  the  current  divides  ;  one 
of  these  is  the  line  circuit,  which  is  of  heavy  wire 
sufficient  to  carry  all  the  current  required  in  the 
exterior  circuit,  and  the  other  is  a  thin  wire  of 
great  length,  and  therefore  of  high  resistance, 
which  is  wound  in  many  turns  around  the  field 
magnet  cores.  Since  this  latter  wire  is  of  high 
resistance,  but  little  current  passes  through  it ;  but 
as  it  passes  many  times  around  the  magnet  there 


FIG.  52. 

are  sufficient  ampere  turns  with  the  small  current 
for  our  purpose.  This  latter  wire,  which  forms  in 
this  case  the  magnet  coils,  is  in  multiple  arc,  or  in 
parallel,  or  "  in  shunt"  with  the  exterior  circuit. 
This  type  is  therefore  called  the  "  shunt  dynamo." 
There  is  a  law  in  the  flow  of  electric  currents  to 
which  we  have  before  referred,  that  when  several 
paths  are  open  to  the  current  the  latter  will  di- 
vide itself  among  them  according  to  the  relative 
conductivities  of  those  paths.  In  Fig.  52  the  cur- 


SEBIES,  SHUNT  AND  COMPOUND  WINDING.      133 

rent  has  two  paths  open  to  it— one  through  the 
fine  wire  of  high  resistance,  which  forms  the 
magnet  coils,  and  the  other  through  the  large  wire, 
which  forms  the  external  circuit.  The  shunt  cir- 
cuit, as  will  be  observed,  is  always  closed,  so  that 
no  matter  whether  the  external  circuit  be  closed 
or  not  a  current  will  always  be  passing  through 
the  field  coils,  and  the  full  magnetism  which  they 
are  capable  of  imparting  to  the  magnet  is  always 
maintained.  The  shunt  dynamo  is  therefore 


FIG.  53. 

peculiarly  fitted  for  multiple  arc  circuits  (street 
railway  and  incandescent  lamp  circuits),  because,  as 
we  know,  multiple  arc  circuits  are  always  open 
when  there  are  no  translating  devices  (lamps, 
cars,  etc.)  operating.  But  if  the  magnetism  of 
the  fields  be  maintained,  the  full  current  is  always 
available  the  moment  it  is  wanted.  But  the 
exterior  circuit  is  one  of  variable  conductivity. 
The  resistance  between  the  trolley  wire  and  the 
ground  is  only  half  as  great  when  two  cars  are 
running  as  when  only  one  is  in  operation.  The 


134 


ELECTEIC   RAILWAY   MOTOES. 


relative  conductivity  of  the  two  paths  therefore 
changes  with  the  number  of  cars  operated,  being 
greatest  in  the  outside  circuit  when  there  are 
many  cars. 

Now  supposing  that  with  the  speed  at  which 
our  armature  is  driven,  and  the  magnetism  which 
the  ampere  turns  of  our  shunt  coils  is  capable  of 
producing,  our  dynamo  is  capable  of  generating 
an  electromotive  force  of  just  five  hundred  volts 
when  but  one  car  is  in  operation.  If  a  second  car 
be  started  up,  the  conductivity  of  the  exterior  cir- 


FIG. 


cuit  will  have  been  increased,  and  it  will  take  a 
relatively  larger  portion  of  the  total  current  gen- 
erated by  the  armature.  This  will  leave  less  to 
go  around  the  magnet  coils,  and  the  magnets 
become  weaker.  With  weaker  fields  the  electro- 
motive force  generated  by  the  same  speed  of 
armature  becomes  less,  and  we  will  no  longer  have 
a  current  of  five  hundred  volts,  but  something 
less  than  that.  This  loss  of  electromotive  force 
is  what  is  technically  termed  "  drop,"  and  while 


THE  REVERSIBILITY  OF  THE  DYNAMO.  135 

in  very  short  lines  with  but  a  car  or  two  operat- 
ing it  may*  not  amount  to  much,  it  becomes  very 
serious  in  long  lines  with  many  cars  or  lights 
to  feed.  To  correct  this  fault  we  sometimes  have 
recourse  to  the  third  method  of  winding,  which  is 
known  as  compound  winding,  and  the  machines 
so  wound  are  known  as  compound  dynamos.  The 
compound  winding  (Fig.  53)  is  a  combination  of 
the  series  and  shunt  windings.  As  shown  in  the 
diagram  the  winding  consists  of  two  coils,  one 
consisting  of  a  few  turns  of  coarse  wire  in  series 
with  the  armature,  through  which  all  the  current 
which  goes  to  the  exterior  circuit  passes,  and  the 
other  consisting  of  the  fine  wire  coils  in  parallel 
or  in  shunt  to  the  latter.  Now  if  we  reduce  the 
resistance  of  the  exterior  circuit  by  putting  on 
additional  cars,  while  we  weaken  the  magnetizing 
effect  of  the  fine  shunt  coils,  as  in  the  last  case, 
the  additional  current  which  is  diverted  to  the 
exterior  circuit,  which  has  to  pass  through  the  series 
coils,  compensates  for  the  other  loss.  By  putting 
on  fewer  or  more  turns  of  the  series  coils  we  may 
exactly  compensate  for  any  loss  of  electromotive 
force  that  might  be  occasioned  in  a  shunt  machine 
by  the  addition  of  cars  or  length  of  line,  or  by 
putting  on  more  turns  than  is  needed,  for  exact 
compensation  may  even  cause  the  electromotive 
force  to  rise  as  the  load  on  the  dynamo  increases. 
A  machine  wound  to  produce  the  latter  effect  is 
said  to  be  "  over  compounded" 

THE    REVERSIBILITY    OF   THE    DYNAMO. 

It  will  have  been  observed  that  heretofore  we 
have  referred  to  the  dynamo  and  to  the  motor  as 
though  they  were  synonymous  terms.  We  have 


136  ELECTRIC    RAILWAY    MOTORS. 

done  this  not  indiscriminately,  but  as  the  one  or 
the  other  served  the  purpose  of  illustration  the 
better.  But  as  a  matter  of  fact  the  dynamo  and 
the  motor  are  one  and  the  same  machine. 

Supposing  we  have  in  a  pipe,  (7,  two  fans  exactly 
alike  (Fig.  54),  each  furnished  with  a  pullejr  by 
which  it  may  be  belted  to  a  line  shaft  or  to  other 
machinery.  If  we  drive  A  rapidly,  it  will  force  a 
current  of  air  through  the  pipe  C  from  A  to  J5, 
and  this  current  of  air  will  cause  JB  to  revolve  like 
a  windmill.  If,  on  the  other  hand,  we  drive  B  by 
its  pulley,  the  current  of  air  which  it  will  produce 
will  drive  A,  and  if  the  current  be  strong  enough 
the  latter,  acting  as  a  motor,  may  drive  other 
machinery  to  which  it  may  be  belted.  In  the  first 
case  we  have  driven  the  fan  A  by  belting  it  to  a 
driving  pulley,  and  it  has  become  a  generator  of  a 
current  of  air  which,  upon  being  conducted  by  the 
pipe  C  to  the  similar  fan  jB,  has  caused  the  latter 
to  revolve  as  a  motor,  rendering  it  capable  of 
driving  other  machinery  through  its  pulley  and 
belt.  In  the  second  case  IB  as  a  generator  drives 
A  as  a  motor. 

It  is  evident  that  these  two  fans  are  perfectly 
reversible  as  regards  their  functions.  By  driving 
either  one  it  becomes  a  generator  of  air  current 
capable  of  driving  the  other  one  as  a  motor.  That 
is  to  say,  if  we  apply  mechanical  energy  to  either, 
it  gives  out  wind  energy,  if  we  may  use  such  an 
expression,  and  if  we  apply  to  it  wincj  energy,  it 
will  give  out  mechanical  energy. 

So  it  is  exactly  with  the  dynamo-electric  ma- 
chine. If  we  drive  the  armature  by  steam  or 
other  power,  the  machine  will  generate  an  electro- 
motive force — electrical  energy;  and  if  we  apply 
electrical  energy  to  its  armature,  the  latter  will 


THE  BEVEBSIBILITY  OF  THE  DYNAMO.          137 

revolve  and  give  out  mechanical  energy.  If 
two  exactly  similar  machines  have  their  Jbrnshes 
connected  by  electrical  conductors,  they  will 
behave  toward  each  other  exactly  as  do  the  fans. 
Since  they  are  exactly  alike,  it  is  immaterial 
which  we  shall  employ  as  a  generator  and  which 
as  a  motor.  If  the  armature  of  one  is  driven,  it 
will  give  rise  to  an  electric  pressure  corresponding 
to  the  pressure  of  air  in  C,  which  by  giving  rise  to 
a  current  will  cause  the  other  to  revolve  as  a 
motor,  the  general  rule  being  that  any  machine 
that  will  make  a  good  generator  will  also  make 
a  good  motor,  and  vice  versa. 

It  will  be  seen  from  the  above  that  the  electric 
motor  bears  the  same  relation  to  the  generator  as 
the  driven  pulley  on  one  shaft  does  to  the  driving 
pulley  on  another,  and  that  the  electric  current 
by  which  the  energy  is  conveyed  from  the  genera- 
tor to  the  motor  performs  the  same  office  exactly 
as  the  belt  does  which  connects  the  driving  pulley 
with  the  driven  pulley.  It  is  perfectly  clear  that 
either  of  two  lines  of  shafting  may  be  used  as  the 
driving  shaft  by  connecting  it  with  the  steam  en- 
gine, and  if  the  pulleys  which  are  belted  together 
on  the  two  shafts  are  of  the  same  size,  it  will  make 
no  difference  in  the  operation  of  the  machinery 
to  which  shaft  it  is  belted,  but  in  mechanical 
operations  it  is  often  desirable  to  give  the  driven 
shaft  a  different  speed  from  that  of  the  line  shaft, 
and  for  that  reason  the  pulleys  on  the  two  shafts 
would  be  given  different  diameters  to  adapt  them 
to  the  required  conditions.  So  in  electrical 
machinery  the  motor  may  differ  radically  in 
appearance,  and  also  differ  somewhat  in  minor 
details,  from  the  generator,  to  better  adapt  it  to 
the  particular  work  it  has  in  hand.  Thus  in 


138  ELECTRIC    RAILWAY   MOTORS. 

the  street  car  motor  compactness  is  a  prime 
requisite,  and  it  is  allowable  to  sacrifice  some 
of  the  requisites  of  a  good  machine  in  order 
that  this  one  feature  may  predominate.  But 
motors  will  not  differ  more '  in  appearance  from 
generators  than  they  do  from  each  other.  While 
the  construction  of  the  two  machines — the  dynamo 
and  motor — may  be  and  frequently  is  the  same,  the 
theory  upon  which  they  operate  is  entirely  differ- 
ent, the  one  being  the  reverse  of  the  other.  The 
same  drawings  are,  however,  entirely  applicable  to 
the  explanation  of  the  motor. 


CHAPTER  XV, 

THE     ELECTRIC    MOTOR* 

WE  have  seen  (Fig.  10,  see  page  60)  that  if  an 
electric  current  is  passed  through  a  coil  of  wire 
it  sets  up  lines  of  force  which  have  a  definite  direc- 
tion within  the  coil  and  give  the  coil  a  distinct 
polarity.  Now  if  this  coil  while  traversed  by  a 
current  of  electricity  be  brought  into  a  magnetic 
field,  viz.,  be  placed  between  the  poles  of  a  magnet, 
it  will  tend  to  take  up  such  a  position  that  the 
lines  of  force  generated  within  its  own  coils  shall 
have  the  same  direction  as  those  of  the  magnetic 
field  in  which  it  is  placed.  That  is,  it  will  tend  to 
place  its  own  axis  directly  on  the  line  joining  the 
north  and  south  poles  of  the  field  magnet,  with  the 
south  pole  of  the  coil  facing  the  north  pole  of 
the  magnet,  and  the  north  pole  of  the  coil  facing 
the  south  pole  of  the  magnet.  In  this  position 
the  coil  presents  the  least  obstruction  to  the  pas- 
sage of  the  lines  of  force  between  the  two  poles  of 
the  magnet,  because  it  presents  the  greatest  area 
for  their  passage,  and  in  fact  assists  the  passage  of 
these  lines  by  the  magnetomotive  force  which  its 
own  current  adds  to  that  of  the  magnet  between 
whose  poles  it  is  placed.  When  the  coil  is  in  the 
position  shown  in  Fig.  23  (see  page  84),  with  a  cur- 
rent traversing  it  in  such  a  direction  as  to  assist 
the  lines  of  force  across  from  ^to  £,  we  have  this 
condition  fulfilled,  and  this  is  the  position  which 

139 


140  ELECTEIC    RAILWAY   MOTOES. 

any  coil  traversed  by  a  current  will  take  up,  if  free 
to  move,  when  placed-  between  the  poles  of  a  mag- 
net. The  usual  way  of  expressing  this  fact  is  to 
say  that  a  closed  electric  circuit  when  placed  in  a 
magnetic  field  tends  to  take  up  such  a  position  as 
to  enable  it  to  embrace  the  greatest  possible  num- 
ber of  lines  of  force.  Clearly  this  condition  is  best 
fulfilled  when  the  plane,  of  the  coil  is  at  right  angles 
to  the  lines  of  force,  as  in  Fig.  23,  and  least  fulfilled 
when  it  is  in  the  position  shown  in  Fig.  22  (see  page 
83),  because  in  the  latter  the  plane  of  the  coil  is 
parallel  to  the  lines  of  force  passing  from  JVto  S, 
and  it  can  embrace  no  lines  of  force  unless  by  some 
means  they  may  be  diverted  from  a  direct  line  so 
as  to  thread  themselves  through  the  loop  in  curved 
lines.  This  they  are  induced  to  do  by  the  current 
in  the  coil,  which  sucks  them  in,  as  it  were,  either 
from  the  upper  side  or  the  lower  side  of  the  coil, 
according  to  the  direction  of  the  current  in  the 
coil.  With  the  current  flowing — as  indicated  by 
the  arrows  in  Fig.  22 — in  the  direction  of  the 
hands  of  a  clock  as  we  look  down  upon  the  coil, 
the  upper  surface  will  have  a  south  polarity — that 
is,  its  own  lines  of  force  will  enter  the  coil  from 
that  side  and  emerge  from  the  lower  side,  which 
will  have  north  polarity.  In  like  manner  some  of 
the  lines  of  force  which  extend  in  straight  lines 
from  JV"to  S  will  be  bent  out  of  the  direct  line  so 
as  to  thread  themselves  through  the  loop  in  the 
same  way.  Other  lines  will  crowd  through,  and 
in  doing  so,  and  in  trying  at  the  same  time  to 
straighten  themselves  out  again,  will  pry  the  loop 
around  from  its  present  position  in  a  direction  con- 
trary to  that  indicated  by  the  arrow.  As  the 
angle  through  which  the  loop  is  thus  turned 
increases  it  permits  still  more  lines  to  thread  it, 


THE    ELECTRIC    MOTOR.  141 

and  these  add  their  prying  effort,  until  the  plane 
of  the  loop  is  at  right  angles  to  the  lines,  which 
permits  the  lines  to  pass  through  without  bending, 
and  therefore  without  further  tendency  to  rotate 
the  coil. 

We  may  note  right  here  one  peculiar  fact:  We 
found  that  when  we  revolved  the  coil  between  the 
poles  N~  S  from  left  to  right  in  the  direction  indi- 
cated by  the  arrow  it  produced  a  current  in  the 
direction  A  B  G  C  D  A.  Now,  if  we  pass  a 
current  through  the  coil  in  the  same  direction  as 
it  took  when  the  coil  was  mechanically  revolved, 
viz.,  DAB  Gr  C  JB,  it  tends  to  cause  the  coil  to 
revolve  in  the  opposite  direction.  That  is  to  say, 
the  current  which  is  generated  by  revolving  a 
coil  in  a  magnetic  field  is  in  such  a  direction  as 
would  cause  the  same  coil  to  revolve  in  the  oppo- 
site direction  :  the  action  of  the  electrical  current 
generated  in  a  coil  is  to  directly  oppose  that  of  the 
motion  which  produced  it.  This  is  a  fundamental 
law  of  electrics,  and  explains  why,  as  the  current 
increases  in  a  circuit,  it  requires  more  force  to 
drive  the  armature  of  the  dynamo.  It  is  because 
the  larger  the  current  traversing  the  coils  of  the 
armature,  the  greater  the  effort  on  the  part  of  that 
current  to  revolve  the  armature  in  the  opposite 
direction,  and  it  is  the  energy  that  is  absorbed  in 
overcoming  this  tendency  that  reappears  in  the 
armature  coils  as  electricity. 

But  to  go  back  a  little  ways.  If  with  the  coil 
in  the  position  shown  in  Fig.  22  we  should  pass 
the  current  in  the  opposite  direction  to  that  indi- 
cated by  the  arrows,  the  lines  would  thread 
through  the  loops  from  the  under  side  and  come 
out  on  the  upper  side,  thus  prying  the  loop  over  in 
the  opposite  direction.  If  at  the  same  time  that 


142  ELECTBIC    BAIL  WAY    MOTORS. 

we  change  the  direction  of  the  current  in  the  loop 
we  also  change  the  direction  of  the  lines  of  force 
in  our  field  by  making  the  right-hand  field  north 
and  the  left-hand  field  south,  we  see  that  the  lines 
will  enter  the  coil  on  the  right  hand  from  below 
and  emerge  on  the  left  hand  from  above,  and 
in  the  effort  to  straighten  themselves  out  will 
again  tend  to  pry  the  loop  in  the  same  direction 
as  in  the  first  case.  We  therefore  see  that  revers- 
ing both  the  magnetism  of  our  fields  and  the 
direction  of  the  current  in  the  armature  has  no 
effect  upon  the  direction  of  rotation  of  the  arma- 
ture. The  direction  of  rotation  will  be  changed, 
however,  if  either  of  them  alone  be  changed. 

If  we  place  a  single  coil  of  wire  traversed  by  a 
current  in  a  magnetic  field  it  will  tend  to  revolve 
about  its  axis  until  the  plane  of  the  coil  is  at 
right  angles  to  the  lines  of  force  of  the  field  in 
which  it  is  placed,  and  the  direction  of  its  rotation 
will  be  determined  by  the  direction  of  the  current 
which  flows  through  the  coil.  No  matter  how 
strong  the  current  or  how  powerful  the  field,  the 
coil  will  not  tend  to  revolve  further  than  90°  from 
the  direction  of  the  lines  of  force.  This  is  entirely 
similar  to  the  action  of  the  compass  needle  when 
a  current-carrying  wire  is  placed  over  it.  We 
remember  that  under  these  conditions  the  needle 
was  deviated  in  one  direction  or  the  other  accord- 
ing to  the  direction  of  the  current  in  the  wire,  and 
tended  to  take  up  a  position  at  right  angles  to  the 
wire.  It  would  be  a  more  general  statement,  but 
equally  true,  that  the  wire  had  an  equal  tendenc\^ 
to  place  itself  at  right  angles  to  the  needle.  The 
action  was  more  apparent  in  the  needle,  however, 
because  that  was  readily  movable,  while  the  coil 
was  not. 


THE    ELECTRIC    MOTOK.  143 

Bat  suppose  we  have  two  coils  of  wire  with 
their  planes  say  at  right  angles  to  each  other,  as 
in  Figs.  30,  32  and  33.  If  the  current  be  diverted 
from  that  coil  which  has  already  been  revolved  to 
*  a  position  at  right  angles  to  the  lines  of  force  of 
the  field,  to  the  other  coil,  which  is  now  parallel 
to  those  lines,  as  may  be  automatically  accom- 
plished by  a  commutator  of  four  parts,  the  rotation 
will  be  continued  in  the  same  direction,  and  we 
have  at  once  an  elementary  electric  motor.  Or  if 
we  have  but  a  single  coil,  as  in  the  first  case, 
whose  ends  terminate  in  a  two-part  commutator, 
and  the  direction  of  the  current  in  the  coil  be  re- 
versed when  it  has  reached  a  position  at  right 
angles  to  the  field,  its  own  lines  of  force  will  be 
reversed  in  direction  and  cause  the  field  lines  to 
seek  a  passage  by  a  circuitous  route  from  the  op- 
posite side  of  the  coil,  and  these,  as  before  stated, 
in  their  endeavor  to  straighten  themselves  out, 
will  pry  the  coil  over  still  further  and  cause  it  to 
make  another  half  revolution. 

In  an  electric  motor  advantage  is  taken  of  both 
of  these  actions  where  there  are  many  coils  at 
various  angles  to  each  other,  and  as  each  coil 
comes  to  the  position  where  the  threading  of  the 
lines  of  force  through  it  in  one  direction  exerts  no 
further  tendency  to  cause  it  to  rotate,  the  current 
in  that  coil  is  reversed  in  direction  so  as  to  cause 
the  lines  to  enter  from  the  opposite  side  and  con- 
tinue to  exert  an  effort  at  rotation.  Thus  by 
changing  the  direction  of  the  current  in  the  coil 
at  the  proper  time  twice  in  each  revolution  a 
single  coil  may  be  kept  in  continuous  rotation. 
But  the  effort  which  will  be  exerted  will  vary 
widely  with  different  positions  of  the  coil  with 
respect  to  the  field.  Twice  in  every  revolution, 


144  ELECTRIC    RAILWAY    MOTORS. 

viz.,  when  the  coil  is  at  right  angles  to  the  field 
the  effort  will  be  nothing,  and  twice,  viz.,  when 
the  coil  is  parallel  to  the  field,  it  will  be  a  maxi- 
mum. We  find  that  these  positions  correspond 
with  the  positions  of  minimum  and  maximum 
activities  of  the  coil  when  used  to  generate  current. 
We  remember  that  in  describing  the  dj^namo  with 
two  coils  at  right  angles  to  each  other  it  was 
stated  that  the  current  would  be  more  uniform, 
for  in  that  case  when  one  coil  was  in  its  neutral 
position  and  cutting  no  lines  of  force,  the  other 
one  would  be  in  the  position  where  it  would 
be  cutting  the  lines  of  force  at  a  maximum 
rate.  So  with  the  motor.  If  we  have  two 
coils  at  right  angles  to  each  other,  one  of  these 
will  be  exerting  its  greatest  effort  at  rotation, 
while  the  other  one  is  exerting  none.  Thus  by 
increasing  the  number  of  coils  at  small  angles  with 
each  other  the  effort  to  turn  the  armature  will  not 
only  be  increased,  but  become  more  uniform.  The 
effort  exerted  by  the  armature  to  revolve  is 
termed  its  "  torque,"  and  is  dependent  upon 
the  number  of  lines  of  force  that  can  be  induced 
to  thread  themselves  through  the  coil,  and  this  is 
dependent,  as  we  know,  upon  the  current.  The 
"  torque  "  of  a  motor,  or  the  effort  which  it  exerts 
to  turn  against  a  resistance,  is  therefore  said  to  be 
dependent  upon  the  amount  of  current  passing 
through  the  armature  coils.  It  is  also,  of  course, 
dependent  upon  the  strength  of  the  field,  but  if 
that  be  constant  it  is  proportional  always  to  the 
current. 


CHAPTER  XVI. 

THE   ELECTRIC  MOTOR. — (Continued.) 

ANOTHER  way  of  explaining  the  action  of  an 
electric  motor,  which  is  simpler,  but  in  most  cases 
not  so  correct,  is  the  following  :  Let  us  suppose 
for  the  moment  that  there  is  but  a  single  coil  on  our 
armature  (Figs.  55  and  56).  If  in  looking  at  the 
commutator  end  of  the  armature  the  current 
passes  through  the  coil  as  it  passes  over  the  end  of 
the  armature  coil  in  the  direction  of  the  arrow 
(Fig.  55),  which  would  be  clockwise  in  the  coil  if 
we  look  at  the  coil  from  the  north  pole  of  the 
magnet,  and  anti-clockwise  if  viewed  from  the 
south  pole,  it  will  make  of  the  armature  core  an 
electromagnet  whose  south  pole  is  near  the  north 
pole  and  whose  north  pole  is  near  the  south  pole  of 
the  field  magnets.  Since  unlike  poles  attract  each 
other,  the  armature  will  tend  to  revolve  until  these 
unlike  poles  are  as  near  together  as  they  can  get, 
or  until  the  axis  joining  the  two  poles  of  the  arma- 
ture is  in  a  straight  line  with  or  parallel  to  the 
axis  joining  the  field  magnet  poles.  If  nothing 
more  were  done,  the  armature  would  simply  os- 
cillate back  and  forth  a  few  times  on  either  side  of 
this  line,  and  finally  come  to  rest  in  the  position 
stated,  just  as  a  compass  needle  does  when  a  mag- 
netic pole  is  brought  near  it,  and  the  attractive 
action  of  the  unlike  poles  upon  each  other  would 
oppose  any  effort  to  move  the  armature  in  either 

145 


146 


ELECTEIC    RAILWAY    MOTOES. 


direction.  But  we  have  seen  that  when  these  four 
poles  are  in  line  the  coil  on  the  armature  is  in  its 
neutral  position,  viz.,  in  that  position  where  in  the 
dynamo  the  electromotive  force  generated  in  the 
coils  changes  direction,  and  where  by  means  of 
the  commutator  it  is  rectified  for  the  exterior 
circuit.  If,  therefore,  a  direct  current  enter  the 
armature  coil  through  the  branches  and  commu- 
tator, its  direction  in  the  coil  will  be  reversed^ 
at  this  point.  Figs.  55  and  56  represent  the  coil 
just  before  and  after  it  has  occupied  this  neutral 
position,  and  the  arrows  show  the  directions  of 
the  currents  under  these  conditions.  It  will  be 


FIG.  55. 


FIG.  56. 


noted  that  just  at  the  moment  when  the  south 
and  north  poles  of  the  armature  have  reached 
the  point  beyond  which  the  mutual  attractions 
between  them  and  the  north  and  south  poles  of  the 
field  magnets  would  no  longer  tend  to  cause  the 
armature  to  revolve,  the  direction  of  the  current 
is  reversed  by  the  commutator,  and  what  were 
the  south  and  north  poles  of  the  armature  become 
the  north  and  south  poles,  and  like  poles  of  the 
machine  are  brought  into  proximity  and  repulsion 
occurs  and  rotation  is  continued.  Thus  by  prop- 
erly arranging  the  coils  and  commutating  the  direc- 
tions of  their  currents  a  continuous  effort,  first 


TORQUE.  147 

of  attraction  and  then  of  repulsion,  is  exerted  upon 
the  armature,  which  causes  it  to  keep  in  continuous 
rotation  and  enables  it  to  do  more  or  less  work  as 
this  pull  and  push  is  large  or  small. 

TOBQUE. 

Now  we  know  that  the  strength  of  a  magnet—- 
viz., the  ability  which  it  evinces  either  to  attract  an 
unlike  pole  or  to  repel  a  like  pole — depends,  other 
things  being  equal,  upon  the  number  of  ampere 
turns  upon  the  magnet.  In  the  case  of  the  motor 
or  dynamo  the  number  of  turns  on  both  the  field 
magnet  and  the  armature  is  fixed,  so  that  the  only 
way  in  which  we  can  vary  the  strength  of  these 
magnets  is  by  increasing  the  current  (remember- 
ing that  the  ampere  turns=number  of  turns  of  the 
wire  X  current  in  amperes).  We  can  therefore 
increase  the  turning  effort  of  the  armature  by 
increasing  the  current  and  thus  increasing  the 
strength  of  the  poles.  This  effort  to  revolve  which 
the  armature  is  able  to-  exert  is  technically  termed 
its  "  torque."  The  torque,  therefore,  is  dependent, 
among  other  things,  upon  the  current,  being 
greater  or  less  as  the  current  in  the  armature  is 
greater  or  less. 

But  everyone  knows  that  in  turning  a  capstan, 
or  in  winding  up  a  heavy  weight  attached  to  a 
rope  on  a  windlass,  it  can  be  moved  much  more 
easily  if  the  crank  arm  or  lever  is  long  than  if  it  is 
short.  In  fact,  to  give  a  concrete  example,  if  our 
windlass  drum  have  a  diameter  of  1  foot  and  the 
load  on  the  rope  be  100  pounds,  this  can  be  exactly 
balanced  by  hanging  on  the  end  of  the  crank  arm  a 
weight  of  10  pounds  if  that  crank  arm  be  10  feet 
long,  and  11  pounds  so  placed  would  draw  the 


148  ELECTEIC    RAILWAY    MOTORS. 

heavier  weight  of  100  pounds  up.  In  this  case  the 
torque  due  to  the  force  of  10  pounds  acting  on  the 
end  of  a  lever  arm  10  feet  long  is  exactly  equal  to  the 
torque  due  to  a  weight  of  100  pounds  acting  at  the 
end  of  a  lever  arm  but  1  foot  long.  Thus  we  see 
that  while  we  can  increase  the  pull  and  push  on 
the  armature  by  increasing  the  current,  we  can 
increase  the  effect  of  this  pull  or  push,  or,  in  other 
words,  make  a  machine  which  will  have  still 
greater  torque,  by  increasing  the  length  of  the 
lever  arm  upon  which  the  torque  due  to  current 
acts.  As  an  example  parallel  to  the  one  cited  of 
the  windlass,  an  armature  ten  feet  in  diameter 
would,  with  the  same  current,  have  ten  times  the 
torque  that  one  but  a  foot  in  diameter  would  have. 
But  in  street  car  motors  our  space  is  limited  and 
we  cannot  far  increase  the  torque  of  our  motor  in 
this  way.  Our  armature  must  necessarily  be  of 
small  diameter,  so  that  our  leverage  is  small.  Nor 
can  we  increase  our  current  indefinitely,  so  other 
means  must  be  resorted  to  to  give  the  motor  suffi- 
cient torque  to  start  a  loaded  car  from  rest  or 
propel  it  up  a  steep  grade. 

It  is  a  law  of  mechanics  that  what  is  termed 
"  work "  is  equal  to  the  product  of  the  force 
(torque)  into  the  space  described  by  it  in  its 
direction  while  overcoming  the  resistance,  and 
"horse  power"  is  the  rate  at  which  this  work  is 
done.  Thus  if  we  have  an  armature  of  small 
diameter  and  small  torque,  it  may  be  able  to  do 
considerable  work  at  a  rapid  rate  if  with  this 
small  torque  it  be  caused  to  revolve  very  fast.  If 
this  were  attached  directly  to  the  axle  of  a  car,  its 
torque  would  not  be  sufficient  to  start  it,  but  if  we 
geared  it  down  through  one  or  more  gears  so  that 
for  every  revolution  of  the  axle  the  motor  would 


TORQUE.  149 

in  the  same  time  have  made  say  fifty  revolu- 
tions, the  torque  on  the  car  axle  would  be  magni- 
fied fifty  times,  and  the  car  would  easily  start  or 
go  up  hill.  It  must  not  be  imagined  that  by 
gearing  down  a  motor  is  enabled  to  do  more  work 
in  a  given  time,  or  that  its  horse  power  is  in  any 
way  increased  thereby,  for  by  the  definition  of 
work  it  is  the  product  "of  the  force  into  the  space 
through  which  it  acts.  If  we  exert  a  small  force 
through  a  very  long  distance  in  a  given  time,  as  is 


FIG.  57. 

the  case  with  the  rapidly  running  armature,  the 
same  horse  power  is  expended  as  if  we  exerted 
fifty  times  as  much  force  through  a  space  one- 
fiftieth  as  long. 

Thus  in  street  car  motors  with  the  small  arma- 
tures and  bipolar  fields  the  necessary  torque  on 
the  car  axle  is  gained  at  the  expense  of  speed  by 
gearing  down.  At  first  all  street  car  motors  were 
double  geared,  but  the  wear  of  these  gears  and 
the  loss  of  power  occasioned  by  them  indicated 


150  ELECTRIC    RAILWAY    MOTORS. 

the  desirability  of  doing  away  with  them  either 
partially  or  wholly.  This  could  only  be  done  by 
increasing  in  some  way  the  torque  on  the  arma- 
ture. Neither  the  diameter  of  the  armature  nor 
the  current  used  could  be  much  increased,  so  re- 
sort was  had  to  the  multipolar  fields.  It  is  very 
clear  that  with  a  four-pole  field  each  of  the  fields 
may  be  made  to  exert  the  same  pulling  or  pushing 
force  on  the  armature  with  the  same  current  as 
is  exerted  by  each  of  the  bipolar  fields  before 
referred  to.  With  four  poles,  therefore,  the  arma- 
ture will  have  double  the  torque,  and  may  there- 
fore run  at  half  the  speed  with  the  same  mechan- 
ical advantage.  This  would  enable  us  to  do  away 
with  one  of  the  two  reduction  gears  of  which  we 
have  spoken,  and  if  we  had  six  poles  and  could 
slightly  increase  the  diameter  of  our  armature,  or 
slightly  increase  the  amount  of  current,  or  both, 
we  could  put  the  armature  directly  on  the  axle 
and  do  away  with  both  gears  and  have  the  same 
axle  torque  as  we  originally  had  with  our  double 
gears.  We  would  have  then  a  single  reduction 
and  gearless  motor  respectively.  It  was  argued 
that  whatever  excess  of  current  might  be  required 
for  the  gearless  motor,  for  instance,  would  be 
more  than  compensated  for  by  the  saving  of  the 
loss  in  the  gears.  As  an  illustration  of  the  gear- 
less  motor  reference  is  made  to  the  subjoined  cut 
of  the  Short  gearless  motor.  It  will  be  observed 
that  its  field  frame  is  triangular  in  section  and 
has  but  three  pole  pieces.  It  is,  however,  a  six- 
pole  machine,  since  the  fields  are  so  wound  as  to 
produce  consequent  poles  in  the  centers  of  each  of 
the  three  parts  of  the  frame  connecting  the  three 
pole  pieces  together. 


CHAPTER  XVII. 

THE   LINE    OF    COMMUTATION. 

HERETOFORE  in  describing  the  action  of  the 
dynamo  we  have  represented  the  two  neutral 
positions  of  the  wire  as  being  on  a  line  at  right 
angles  to  the  axis  of  the  pole  pieces  (see  Figs.  26  and 
28,  see  pages  87  and  89).  This  would  only  be  the 
case,  however,  when  there  was  no  current  in  the 
armature.  Let  us  examine  what  would  happen  in 
a  motor  armature,  when  a  current  is  passing  in  its 
coils.  If  it  be  a  closed  coil  armature,  such  as  is  now 
almost  universally  used  on  street  cars,  the  current 
passing  through  the  armature  coils  will  tend  to  make 
north  and  south  poles  on  the  armature,  which  will 
be  at  the  ends  of  a  diameter  at  right  angles  to 
that  which  joins  the  north  and  south  poles  in- 
duced in  the  armature  by  the  magnetism  of  the 
fields.  Since  under  the  circumstances  there  can- 
not be  more  than  two  poles  in  the  armature,  there 
will  be  a  compromise  between  the  north  and  south 
poles  produced  by  the  armature  coils  and  the  cor- 
responding north  and  south  poles  induced  by  the 
field  magnets.  Should  these  two  sets  of  poles  be 
of  exactly  equal  strength,  the  compromise  poles 
will  be  halfway  between  the  two,  and  the  line  of 
commutation  (the  line  which  joins  the  positions 
where  the  individual  coil  is  generating  no  electro- 
motive force)  will  be  at  right  angles  to  the  line 
joining  the  compromise  poles,  and  the  brushes 

151 


152  ELECTRIC    RAILWAY    MOTORS. 

must  be  moved  to  this  new  position,  else  they  will 
pass  from  one  commutator  segment  to  the  next 
while  there  is  a  difference  of  potential  between 
them,  which  will  cause  sparking. 

If  the  induced  poles  are  relatively  stronger  than 
the  poles  produced  by  the  armature  current, 
which  would  be  the  case  if  the  armature  current 
is  weak  compared  with  the  field  strength,  the  com- 
promise poles  would  approach  more  nearly  to  the 
induced  poles,  and  if  the  field  magnets  were  very 
overpowering  in  their  strength,  the  compromise 
poles  would  nearly  coincide  with  the  induced 
poles,  and  the  line  of  commutation  would  nearly 
coincide  with  that  which  we  have  provisionally 

fiven  it,  viz.,  at  right  angles  to  a  line  joining  the 
eld  magnet  poles.  But  as  a  motor  is  called  upon 
to  do  more  or  less  work,  the  current  admitted  to 
its  coils  must  be  increased  or  decreased.  This 
results,  of  course,  in  strengthening  or  weakening 
the  resulting  poles.  The  position  of  the  com- 
promise poles  will  therefore  be  constantly  chang- 
ing, which  means,  of  course,  that  the  line  of  com- 
mutation is  constantly  shifting.  It  has  already 
been  explained  that  to  prevent  sparking  the 
brushes  must  bear  on  the  armature  on  the  line 
of  commutation,  so  the  brushes  must  be  shifted 
as  that  changes.  By  making  the  armature  poles 
weak  relative  to  the  field,  considerable  change  of 
current  in  the  armature  may  occur  without  much 
shifting  of  the  neutral  line,  and  under  these  cir- 
cumstances it  may  operate  through  quite  a  range 
of  work  with  fixed  brushes  without  sparking.  It 
is  because  of  an  abnormal  rush  of  current  through 
the  armature  on  starting  up  a  car,  resulting  in  an 
abnormal  shifting  of  the  neutral  line,  that  the 
sparking  in  street  car  motors  occurs.  Since  the 


COUNTER    ELECTROMOTIVE    FORCE.  153 

street  car  motor  is  called  upon  to  operate  through 
an  exceedingly  wide  range  of  work,  the  field 
magnets  are  made  the  dominating  «ffig  «o  as  to 
Keep  tlie  neutral  line  very  'nearly  stationary 
throughout  this  range.  In  series  motors,  however, 
if  neither  armature  nor  field  is  near  saturation,  the 
neutral  line  will  not  change  its  position. 

COUNTER    ELECTROMOTIVE    FORCE. 

Considerable  space  was  devoted  to  explaining 
and  emphasizing  the  fact  that  if  a  closed  loop  of 
wire  be  revolved  around  its  axis  between  the  poles 
of  a  magnet,  or,  in  other  words,  is  revolved  in  a 
magnetic  field,  so  that  its  rate  of  cutting  the  lines 
of  force  is  constantly  changing,  it  will  generate  an 
electromotive  forces 

It  is  perfectly  apparent  that  when  we  operate 
a  motor  by  passing  current  through  it  from  one 
brush  to  the  other  we  are  fulfilling  all  of  these 
conditions,  and  the  coils  of  the  motor  armature 
must  also  develop  an  electromotive  force.  It 
makes  no  difference  whether  an  armature  is 
driven  by  electricity  or  by  steam  power,  if  its 
coils  revolve  in  a  magnetic  field,  there  will  be  gen- 
erated in  them  an  electromotive  force.  In  the 
case  of  the  motor,  however,  this  electromotive 
force  is  in  the  opposite  direction  to  that  of  the 
current  which  operates  the  motor,  and  is  there- 
fore called  the  "  counter  "  electromotive  force.  It 
follows  exactly  the  same  laws  as  govern  the  gen- 
eration of  electromotive  forces  in  dynamos,  and 
will  be  the  higher  the  greater  the  speed  of  the 
armature.  A  motor  running  at  high  speed,  as  it 
will  if  allowed  to  when  it  is  running  without  load, 
will  generate  a  counter  electromotive  force  almost 


> 

(UNIVERSITY 

V 


154  ELECTKIC    RAILWAY   MOTORS. 

equal  to  that  of  the  current  by  which  it  is  operated, 
and  will  therefore  take  but  very  little  current. 
The  current  that  a  motor  will  take  under  any 
conditions  is  that  which  is  due  to  the  difference 
between  the  direct  electromotive  force  of  the 
current  and  the  counter  electromotive  force  of  the 
motor  itself.  The  counter  electromotive  force  of 
a  motor  at  any  speed  is  exactly  equal  to  that  which 
the  same,  motor  would  generate  if  driven  as  a 
dynamo  at  the  same  speed.  If,  therefore,  a  motor 
is  starting  from  rest,  it  has,  at  first,  no  counter 
electromotive  force.  The  only  obstacle  to  the  flow 
of  current  through  the  armature  would  be  the 
resistance  within  the  machine  itself,  which,  being 
exceedingly  small,  would,  according  to  Ohm's  law, 
permit  an  enormous  current  to  flow  through  its 
coils,  which  would  inevitably  result  in  a  burn  out 
if  it  were  not  checked.  This  is  the  reason  why  a 
rheostat  is  almost  universally  used  in  starting. 
It  opposes  at  first  a  great  artificial  resistance,  and 
this  is  decreased  as  speed  is  gained  and  counter 
electromotive  force  is  generated,  when  all  artificial 
resistances  may  be  removed  writh  impunity. 

This  back  electromotive  force  of  a  motor  has 
its  exact  counterpart  in  the  resistance  which  the 
armature  of  a  dynamo  offers  to  the  driving  engine. 
We  all  know,  or  can  find  out  for  ourselves,  that 
when  a  dynamo  is  generating  no  current,  as,  for 
instance,  when  the  armature  is  not  irr  motion, 
we  can  readily  turn  the  armature  with  the  hand, 
and  yet  when  it  is  working  to  its  utmost  capacity 
it  may  take  hundreds  of  horse  power  to  keep  it 
in  rotation.  This  resistance  to  the  mechanical 
effort  of  the  steam  engine  is  really  the  measure  of 
the  work  the  dynamo  is  performing  ;  so  the  elec- 
trical resistance  opposed  by  the  counter  electro- 


COUNTER    ELECTROMOTIVE    FORCE. 


155 


motive  force  of  the  motor  is  a  measure   of   the 
work  the  motor  is  doing. 

Professor  Silvauus  Thompson,  in  his  great  work 
on  "  Dynamo-Electric  Machinery,"  cites  an  ex- 
ample which  very  well  shows  how  the  current  that 
a  motor  will  take  decreases  with  the  speed  of  its 
armature.  He  used  a  small  Immisch  motor  with 
separately  excited  fields,  and  connected  it  up  with 
a  primary  battery  and  amperemeter.  At  different 
speeds  the  following  figures  were  obtained  : 


Speed  Revs, 
per  Minute. 

o 

Current 
Amperes. 
20 

Speed  Revs, 
per  Minute. 
160 

Current 
Amperes. 

78 

50 

.    162 

180 

.     .  .          61 

100.. 

..12.2 

195.. 

..5.1 

Thus  at  its  maximum  speed  it  took  only  about 
one-fourth  of  the  current  that  it  took  when  the 
armature  was  held  at  rest.  In  this  case  5.1  am- 
peres were  required  to  overcome  the  friction  of 
the  armature.  Had  the  friction  been  less  the 
armature  would  have  revolved  still  faster  and 
finally  come  to  constant  speed  with  less  current 
than  5.1  amperes. 

In  the  earlier  days  of  the  electric  motor  this 
counter  electromotive  force  was  a  bugbear  and 
thought  to  be  an  objectionable  feature,  and  at- 
tempts were  made  to  construct  motors  from  which 
it  would  be  eliminated.  But  we  now  know  that 
the_(£xistence^  of  this  counter  electromotive  force 
is  of  the  utmost  importance,  and  that  upon  it  de- 
pen  ds  the  degree  to  which  any  given  motor 
enables  us  to  utilize  electric  energy  that  is  sup- 
plied to  it  in  the  form  of  an  electric  current.  "In 
fact,"  says  Professor  Thompson,  "  this  countei 
electromotive  force  is  an  absolute  and  necessary 
factor  in  the  power  of  the  motor,  just  as  much  as 


156  ELECTRIC    BAIL  WAY   MOTORS. 

the  velocity  to  which  (other  things  being  equal)  it 
is  proportional." 

As  will  be  seen  from  the  figures  given  by  Pro- 
fessor Thompson  and  the  subsequent  remarks,  the 
amount  of  current  that  a  motor  will  take  is  only 
that  which  is  absolutely  necessary  to  do  the  work 
which  it  is  called  upon  to  do.  That  is  to  say,  if 
it  has  no  other  work  to  do  than  to  overcome  its 
own  friction,  its  armature  will  automatically 
attain  such  a  speed  as  to  generate  a  counter 
electromotive  force,  or  "  back  "  pressure,  such  that 
only  sufficient  effective  electromotive  force  remains 
to  force  through  the  motor  sufficient  current  to 
move  the  armature  against  this  resistance.  If 
now  an  additional  load  is  thrown  on  the  motor, 
the  speed  of  its  armature  will  be  at  once  retarded, 
less  counter  electromotive  force  will  be  generated, 
and  consequently  more  current  will  pass,  and  the 
motor  at  once  adjusts  itself  to  this  new  load. 


CHAPTER  XVIII. 

COUNTER    ELECTROMOTIVE    FORCE    AND    SPEED 
REGULATION. 

BUT  this  counter  electromotive  force  must  not 
be  confounded  with  dead  resistance.  It  has  in 
some  respects  the  same  effect  as  resistance,  but 
differs  from  the  latter  in  very  important  particu- 
lars. It  has  been  stated  that  counter  electro- 
motive force  cuts  down  the  current.  Resistances 
placed  in  circuit  will  do  the  same  thing  exactly," 
but  the  cutting  down  of  current  by  means  of  the 
counter  electromotive  force,  which  tends  to  pro- 
duce a  current  in  the  opposite  direction,  is  merely 
a  problem  in  subtraction — the  taking  of  a  lesser 
quantity  from  a  greater,  and  the  utilization  of  the 
remainder.  No  energy  whatever  is  consumed 
when  the  current  is  reduced  in  this  way,  but 
when  it  is  reduced  by  the  use  of  resistances  the 
electromotive  force  which  disappears  is  employed 
in  overcoming  these  resistances,  and  the  energy 
thus  expended  appears  as  heat.  In  electric  light- 
ing, welding,  etc.,  this  energy  is  usefully  expended, 
for  by  designedly  localizing  the  resistance  we 
localize  the  heat  to  such  an  extent  as  to  produce 
the  desired  results  of  high  temperatures.  But  in 
most  other  applications  of  electricity  it  is  not  heat 
that  we  want,  but  mechanical  energy.  Every  bit 
of  heat  that  is  generated  in  our  circuit  or  in  our 
translating  devices,  therefore,  represents  so  much 

157 


158  ELECTEIC    RAILWAY   MOTORS. 

energy  uselessly  employed,  and  constitutes  a  drain 
upon  our  source  of  energy  for  which  we  have  to 
pay  as  much  as  we  pay  for  the  energy  which  serves 
a  useful  purpose.  The  heat  produced  in  an 
electric  circuit  corresponds  very  closely  to  the 
water  lost  in  a  leaky  water  main  along  the  route. 
If  the  pipe  be  very  leaky,  half  the  water  that  is 
pumped  into  it  at  the  pumping  station  may  leak 
out,  and  while  it  does  the  consumer  at  the  other 
end  of  the  line  no  good,  costs  at  the  pumping 
station  just  as  much  as  the  other  half  does  which 
he  can  make  use  of.  Where  an  electric  motor 
heats  up  badly,  or  resistances  are  introduced  into 
the  circuit  near  the  motor  in  order  to  cut  down 
the  current  to  the  required  amount,  they  consti- 
tute large  leaks  which,  in  the  water  analogy,  would 
correspond  to  the  diversion  of  a  portion  of  a 
waterfall  from  a  water  wheel  so  as  to  let  that  por- 
tion diverted  run  to  waste,  or  where  the  water  is 
conveyed  to  a  water  motor  in  a  pipe,  to  the  open- 
ing of  a  large  faucet  just  above  the  water  motor, 
so  that  a  portion  only  of  the  water  that  was  de- 
livered at  that  point  would  go  to  the  motor,  the 
remainder  being  allowed  to  run  out  upon  the 
ground. 

But  it  is  often  necessary  with  electric  motors 
to  resort  to  these  wasteful  methods  of  regulation. 
As  everyone  knows,  it  requires  the  expenditure 
of  considerable  energy  to  set  in  motion  any  body 
which  is  at  rest,  and  it  also  requires  the  expendi- 
ture of  this  energy  for  a  considerable  time  before 
that  body — especially  if  it  be  a  heavy  body — can 
be  set  into  very  rapid  motion.  Everyone  also 
knows  that  when  the  moving  body  has  once  at- 
tained a  certain  speed  this  same  speed  can  be 
maintained  with  the  expenditure  of  but  a  very 


COUNTER   ELECTROMOTIVE   FORCE.  5 

small  fraction  of  the  energy  required  to  bring  it 
up  to  that  speed.  The  same  is  true,  in  a  reverse 
order,  of  bringing  a  moving  body  to  rest.  This 
property,  which  is  characteristic  of  all  matter,  by 
which  it  resists  any  change  as  regards  motion  or 
rest,  is  termed  inertia,  and  the  heavier  the  body 
is  the  longer  must  a  given  force  act  upon  it  to 
start  it  from  a  state  of  rest  and  bring  it  to  a  given 
speed,  or  to  check  it  from  a  given  speed  and  bring 
it  to  rest.  We  therefore  see  why  in  electric 
motors  it  is  necessary  in  starting  them  to  reduce 
the  current  by  what  have  been  termed  dead  or 
hurtful  resistances,  for  when  the  armature  is  at 
rest  there  is  of  course  no  counter  electromotive 
force  to  oppose  the  current.  The  only  resistance 
opposed  to  its  flow  at  this  instant  is  that  which 
is  offered  by  the  coils  on  the  armature  (and  fields 
in  the  case  of  series  winding),  and  this  has  been 
made  by  the  builder  as  small  as  possible  purposely 
to  prevent  the  loss  of  energy  which  resistances 
necessarily  involve.  If,  therefore,  the  current 
were  turned  on  full  from  a  five  hundred  volt  cir- 
cuit, the  momentaiy  rush  would  be  so  great  as  to 
burn  the  motor  up  at  once. 

To  realize  how  quickly  the  heating  effects  in- 
crease with  the  current  we  need  only  to  remember 
the  law  that  the  heat  thus  produced  is  propor- 
tional to  the  square  of  the  current.  It  would  be 
bad  enough  under  these  circumstances  if  double 
and  treble  the  current  produced  only  double  and 
treble  the  heat,  for  a  motor  in  starting  may  take 
ten  times  the  amount  of  current  that  it  would 
require  when  doing  the  full  work  for  which  it  was 
designed,  but  when  we  remember  that  the  heat 
will  be  increased  to  four  times  and  nine  times  for 
double  and  treble  the  current,  and  one  hundred 


160 


ELECTKIC    RAILWAY   MOTORS. 


times  for  ten  times  the  current,  the  seriousness  of 
such  a  situation  will  be  realized  at  once. 

Some  means  must  therefore  be  resorted  to  to 
prevent  this  enormous  rush  at  starting,  and  the 
one  usually  employed  is  dead  resistance.  A  large 
resistance,  sufficient  to  cut  the  current  down  to 
the  safe  amount,  is  first  introduced.  As  the 
armature  starts  to  revolve  it  immediately  begins 
to  generate  a  slight  counter  electromotive  force. 
By  reason  of  this  the  full  amount  of  the  original 
resistance  is  no  longer  required  to  maintain  the 
same  current,  and  a  smaller  resistance  may  be 
substituted.  As  the  speed  of  the  armature  in- 


FIG.  58. 


creases  so  does  the  counter  electromotive  force, 
and  in  like  manner  does  the  necessity  for  dead 
resistance  decrease.  In  fact,  with  the  speed  of  the 
armature  the  counter  electromotive  force  gradually 
usurps  the  functions  of  the  resistance  until  the 
speed  has  reached  that  at  which  the  motor  was 
designed  to  run,  when  it  will  have  supplanted  it 
entirely. 

To  facilitate  the  introduction  into  the  motor 
circuit  of  resistances  of  various  values  as  re- 
quired, such  resistances  are  usually  grouped  to- 
gether and  their  terminals  so  connected  that  any 
one  or  more  of  them  may  be  thrown  into  circuit 


REQUIREMENTS    OF    SPEED    REGULATION.         161 

by  the  movement  of  a  lever.  Such  an  arrange- 
ment is  called  a  rheostat,  and  such,  in  fact,  is  the 
arrangement  on  the  platforms  of  electric  cars  to 
which  the  controlling  lever  is  attached  by  which 
the  motorman  controls  his  car. 

The  desire  to  avoid  as  much  as  possible  the 
losses  necessarily  involved  in  the  "  rheostat  regu- 
lation "  of  current  as  well  as  the  requirements  for 
speed  regulation,  so  essential  in  street  cars,  has 
resulted  in  numerous  other  arrangements,  which 
will  be  referred  to  after  we  have  considered  what 
the  requirements  of  speed  regulation  involve. 

THE    REQUIREMENTS     OF     SPEED     REGULATION. 

In  discussing  this  question  it  will  be  under- 
stood, of  coursje,  that  we  are  not  speaking  of  how 
to  build  motors  suitable  for  various  speeds,  but 
how  to  regulate  the  speed  of  motors  already  built 
or  in  use.  We  must,  therefore,  take  the  motor 
as  we  find  it,  viz.,  with  certain  elements,  such  as 
the  number  of  turns  of  wire  on  the  armature, 
which,  if  changed,  would  modify  the  speed,  fixed. 
We  cannot  do  better  on  this  subject  than  to  quote 
from  Crosby  and  Bell's  most  excellent  treatise  on 
"  The  Electric  Railway,"  which  those  wishing  to 
go  more  deeply  into  the  subject  of  electric  rail- 
ways than  it  is  intended  to  do  in  this  volume 
should  certainly  read : 

"  The  other  quantities,  changes  in  which  are  con- 
nected with  changes  in  speed,  are  (1)  strength  of 
field,  (2)  the  rate  of  work,  i.  e.,  the  quantity  of 
work  done  in  a  given  time.  As  has  been  already 
shown,  the  rate  of  work  is  measured  by  the  prod- 
uct of  (3)  the  current  and  (4)  the  counter  elec- 
tromotive force.  The  current,  however,  is  readily 


162  ELECTEIC    RAILWAY   MOTORS. 

expressed  in  terms  of  the  counter  electromotive 
force,  the  resistance  of  the  machine  and  the 
applied  electromotive  force,  since  it  is  always  such 
a  current  as  will  flow  over  the  given  resistance 
under  a  pressure  equal  to  the  difference  between 
the  two  opposing  pressures — that  applied  or  im- 
pressed by  the  dynamo  through  the  line,  and  that 
generated  by  the  motor  armature  itself.  (5)  As 
seen  from  the  above,  change  in  the  applied  E.  M.  F. 
is  also  connected  with  change  in  the  speed.  The 
quantities  (1),  (2),  (3),  (4),  (5)  are  interdependent, 
but  are  separately  mentioned,  since  convenience 
requires  reference  first  to  one,  then  to  another. 

"  Of  these  five  quantities  perhaps  that  which  in 
practice  is  most  constant  is  strength  of  field.  As 
has  been  shown,  the  efficiency  of  a  motor  depends 
upon  the  relation  of  the  counter  E.  M.  F.  to  the 
applied  E.  M.  F.  High  efficiency  or^jnelajrixelj 
high  counter  E.  M.  F.  is  desirable  at  any  and  all 
speeds.  But  BTgK^counter E.  M.  F.  goes  wltli~a 
large  product  of  the  three  factors  :  (a)  number 
of  armature  loops,  (b)  speed  of  rotation  and  (c) 
strength  of  field.  As  noted  («),  the  number  of 
loops  is  fixed,  (b)  the  speed  is  limited  by  practical 
requirements,  hence  (c)  great  strength  of  field  is 
constantly  desirable.  It  is  therefore  good  prac- 
tice so  to  wind  a  street  railway  motor  by  putting 
a  relatively  large  number  of  turns  around  its 
magnet  that  a  maximum  strength  of  field  is  at- 
tained, even  when  the  current  flowing  is  small  as 
compared  with  the  maximum  current. 

"  This  is  equivalent  to  saying  that  the  magneti- 
zation given  by  a  relatively  small  current  is  yet 
sufficient  to  saturate  or  nearly  saturate  the  iron  .of 
the  magnetic  circuit.  If,  however,  the  field  be 
kept  below  saturation  and  be  varied  in  strength, 


REQUIREMENTS    OF    SPEED   REGULATION.         163 

this  variation  may  be  used  to  accomplish  a  cer- 
tain degree  of  speed  regulation.  Let  us  suppose 
a  car  moving  on  a  level  (or  on  a  uniform  grade) 
and  at  such  a  speed  as  to  produce  a  counter  E. 
M.  F.  of  400,  the  applied  E.  M.  F.  being  500. 
For  convenience  assume  the  internal  resistance 
of  the  armature  circuit  to  be  10  ohms.  Then  the 
current  flowing  will  be 
500—400  impressed  E.  M.  F. — counter  E.  M.  F. 

10  resistance 

100 

=  10  amperes. 

10 

The  mechanical  work  done  would  be  400X10=E. 
XC.= impressed  E.  M.  F.X  current =4000  watts. 

"  Now  supposexit  is  desired  to  run  more  slowly. 
Increase  the  field  strength  by  ten  per  cent.  The 
counter  E.  M.  F.  at  the  same  speed  would  be  44*0 
volts. 

500—440 

The  current = =6  amperes, 

10 

and  the  work,  440X6=2640  watts.  But  since  the 
car  requires  4000  watts  to  maintain  the  previous 
speed,  it  is  now  evident  that  it  must  now  decrease 
its  speed  until  there  shall  be  an  equality  between 
the  work  required  to  maintain  the  lower  speed 
and  the  work  done  by  the  motor  at  the  lower  speed 
due  to  the  greater  field  strength.  Let  us  learn 
what  this  speed  is. 

"  It  was  seen  above  that  work  at  the  rate  of 
4000  watts 
4000 

(= =5.36  H.  P.  =  176,880  foot  pounds  per  min.) 

746 


164  ELECTEIC   RAILWAY   MOTORS. 

must  be  performed  in  order  to  maintain  the  speed 
existing  before  the  change  of  field  strength.  Sup- 
pose the  car  to  weigh  8  tons,  and  suppose  that  on 
the  particular  track  in  question  a  horizontal  effort 
of  25  pounds  per  ton  is  required  to  overcome  all 
resistances,  including  those  of  gears  or  other 
mechanism  between  the  armature  and  the  axles  ; 
then  a  total  horizontal  effort  of  8  X  25  =  200  pounds 
must  have  been  exerted.  This  quantity  multiplied 
by  the  number  of  feet  traveled  per  minute  must 
be  equal  to  the  number  176,880,  representing  the 
total  foot  pounds  of  energy  utilized  per  minute. 
Hence  the  travel  per  minute 
176,880 

==_ =884.4  feet==10.05 

200 

miles  per  hour.     At  the  new  speed  we  must  have 
a  similar  relation,  viz., 

work  done  in  foot  pounds 


200 

feet  traveled  per  minute  ;  or  since  1  watt  minute 
=44.24  foot  pounds. 

work  in  watts 


;  200-7-44.24}  "-Hi 
feet  traveled  per  minute  ;  hence  the  work  in  watts 
=4.52  X  feet  traveled  per  minute."  -  *fS5«7  fj^ 
It'will  be  observed  from  the  above  that  a  reduc- 
tion in  speed  results  from  increasing  the  strength 
of  the  field.  The  converse  is  also  true,  viz.,  that 
a  weakening  of  the  field  results  in  increased  speed. 
This  latter  can  be  readily  proved  by  placing  an 
iron  bar  across  the  pole  pieces  of  a  stationary 
motor,  thus  diverting  some  of  the  lines  of  force 
from  the  armature.  A  very  noticeable  increase  of 


it  i/o  =  WAX 

'vy" 


REQUIREMENTS    OF   SPEED    REGULATION.         165 

speed  of  armature  will  at  once  occur  due  to  the 
weakening  in  this  way  of  the  field  in  which  the 
armature  is  working. 

Thus  far  we  have  assumed  that  the  car  is  run- 
ning upon  a  level  track  or  up  a  uniform  grade,  or, 
in  other  words,  that  the  work  the  motors  are 
called  upon  to  perform  remains  constant. 

Of  course  if  the  load  be  increased,  more  energy 
is  required  to  move  it  at  the  same  speed — a  greater 
torque  will  be  required  in  the  armature,  and  this 
may  be  accomplished  by  increasing  the  current  in 
the  latter,  as  already  stated.  The  conditions  for 
maintaining  uniform  speed  under  increased  load, 
therefore,  are  obtained  by  a  relatively  large  increase 
of  armature  magnetism  over  field  strength.  Thus 
in  a  shunt  motor  operating  under  constant  E.  M. 
F.  the  strength  of  the  field  remains  constant  under 
all  conditions  of  work,  while  the  armature  current 
may  vary  within  wide  limits,  and  does  vary  directly 
as  the  load.  But  in  a  series  wound  motor,  such  as 
is  usually  employed  on  street  cars,  since  all  the 
current  passing  through  the  armature  also  passes 
around  the  field,  the  magnetism  of  both  will  con- 
tinue to  increase  in  about  the  same  ratio  until 
either  one  or  the  other  becomes  saturated,  after 
which  its  magnetism  cannot  increase  further  and 
remains  stationary,  while  the  other  increases  with 
additional  current.  It  has  already  been  stated 
that  in  street  railway  motors  it  is  customary  to 
make  the  fields  relatively  stronger  than  the  arma- 
ture. '  This  is  done  by  making  so  many  turns  in 
the  field  magnet  coils  that  with  the  currents  usu- 
ally employed  the  field  magnets  are  nearer  a  state 
of  saturation  than  the  armature.  If  this  be  the 
case  in  a  series  motor,  and  sufficient  load  be  thrown 
on  to  slacken  the  speed  of  the  motor  and  thereby 


166  ELECTEIC   EAILWAY   MOTOES. 

lower  the  counter  E.  M.  F.,  sufficient  additional 

current  will  pass  to  saturate  the  field.     Should  the 

speed  become  still  slower,  more  current  would  pass, 

but  the  field,  being  already  saturated,  would  not  be 

further  increased  in  strength,  while  the__arm_ature 

strength   would   be   still   furtheF  increased,   thus 

I    fulfilling   the   conditions   of  relative   increase   of 

I  'armature   ovg*'  field  required   for  greater  speed, 

\  and~tFe   motor   would   run   faster   until    the  in- 

\  crease   of   counter  E.   M.    F.   resulting  f  ronPlts 

/Increased  speect "restores  a  balance  and  the  speed 

remains  constant. 

Thus  far  we  have  considered  all  the  windings 
on  the  field  magnet  to  constitute  one  integral  coil. 
Much  greater  elasticity  or  flexibility  of  control 
may  be  obtained  by  winding  the  field  magnet  with 
a  number  of  separate  coils  which  may  be  connected 
up  in  various  ways  so  as  to  be  used  separately,  in 
series  or  in  multiple  arc,  thus  enabling  the  motor- 
man  to  change  the  relative  strengths  of  field  and 
armature  through  a  much  wider  range.  This  will 
be  made  clear  by  reference  to  Fig.  59  (see  page 
160)  and  the  following  explanation. 

Suppose  three  coils  of  wire  to  be  wound  around 
the  magnet  cores  of  a  motor,  as  shown  in  Fig.  59. 
Let  the  resistance  of  each  be  1  ohm.  Connect 
D  to  B  and  12  to  C  (so  that  the  three  coils  are  in 
series).  Suppose  a  difference  of  potential  of  100 
volts  be  maintained  between  the  terminals  A  and 
F  •  then  the  total  resistance  of  this  field  circuit 
would  be  3  ohms.  The  current  flowing  would  be 
100 

=33.3  amperes. 

3 

The  number  of  turns  in  each  coil  is  two — one  on 
each  leg.     There  will  therefore  be  six  coils  in  all, 


REQUIREMENTS   OP   SPEED   REGULATION.        167 

and  the  magnetizing  effect  expressed  in  ampere 
turns  would  be  33.3X6  =  199.8. 

If,  however,  we  connect  the  three  coils  up  in 
parallel  by  connecting  A,  B  and  C  together  and 
D,  E  and  F  together,  the  resistance  of  the  field 
circuit  would  be  one-third  of  an  ohm  instead  of 
three  ohms  as  before,  and  the  current  flowing 
would  be  100-i-^=300  amperes  instead  of  33.3, 
and  the  number  of  turns  around  which  this  whole 
current  would  flow  would  be  but  two,  and  the 
resulting  magnetizing  effect  expressed  in  ampere 
turns  would  be  300X2=600,  or  three  times  the 
former  value. 

If  sufficient  current  passed  through  the  coils 
when  arranged  in  series  to  saturate  the  field,  no 
further  magnetism  would  be  added  to  the  field  by 
the  second  arrangement,  but  the  strength  of  the 
armature,  if  that  were  far  from  saturation,  would 
be  proportionately  increased,  as  well  as  relatively 

fiving  the  latter  a  greater  torque  as  well  as  a  ten- 
ency  by  reason  of  a  relatively  weaker  field  to 
greater  speed  ;  but  even  if  the  field  also  be  far 
from  saturation  with  the  first  arrangement,  and  its 
strength  increases  proportionately  with  the  addi- 
tional ampere  turns  of  from  199.8  to  600,  which 
would  result  from  the  second  arrangement,  the 
drop  of  potential  required  to  force  a  given  current 
through  the  field  windings  would  be  much  less  in 
the  second  arrangement  than  in  the  first  because 
of  the  lessened  resistance  (in  this  case  3 — £=2f 
ohms),  and  the  electromotive  force  in  the  armature, 
if  the  latter  be  placed  in  series  with  the  field  coils, 
would  be  greater  in  the  second  arrangement  than 
in  the  first,  again  fulfilling  the  conditions  neces- 
sary to  greater  speed.  It  is  evident  that  other 
combinations  of  these  coils  may  be  employed  to 


168  ELECTRIC   RAILWAY   MOTORS. 

produce  different  results.  Thus  in  starting  all 
three  coils  may  be  put  in  series,  then  one  may  be 
cut  out  and  the  other  two  connected  in  series,  and 
next  the  two  in  multiple  with  each  other  and  in 
series  with  the  third,  then  two  in  multiple  with 
the  third  cut  out,  and  finally  the  second  arrange- 
ment above  described — all  three  in  multiple.  The 
various  changes  above  enumerated — changes  of 
connections — from  first  to  last  are  progressively 
toward  the  attainment  of  higher  speeds.  This 
method  of  regulation  is  known  as  that  by  "  corn- 
mutated  field  circuits." 

On  most  street  cars  there  are  two  motors.  It  is 
evident  that  with  two  motors  the  commutation 
method  of  control  can  be  still  further  extended  by 
throwing  the  coils  of  the  two  motors  not  only  into 
the  above  combinations  with  the  other  coils  on  the 
same  motors,  but  by  throwing  the  coils  of  one 
motor  into  various  combinations  with  the  coils  on 
the  other.  Thus  in  starting  all  the  coils  on  both 
motors  would  be  throwrn  into  series,  and  these  in 
series  with  the  armature  coils  of  both  motors, 
themselves  in  series  with  each  other,  and  so  by 
various  changes  gradually  decreasing  the  resistance 
of  the  field  circuits  until  all  the  field  coils  in  each 
motor  are  in  multiple  with  each  other,  and  the  two 
motors  are  in  multiple  with  each  other,  which 
would  be  the  condition  for  maximum  speed. 


CHAPTER  XIX. 

THE    SPERBY   AND    JOHXSON-LUNDELL    SYSTEMS. 

THERE  has  existed  quite  a  difference  of  opinion 
among  electricians  as  to  the  relative  merits  of 
rheostat  and  commutated  field  control,  but  the 
discussions  which  have  taken  place  in  the  Ameri- 
can Institute  of  Electrical  Engineers  and  in  the 
technical  periodicals  on  the  merits  of  the  two 
systems  have  apparently  resulted  in  no  conver- 
sions on  either  side.  They  have  resulted,  how- 
ever, in  making  us  better  acquainted  with  the 
demerits  of  each,  many  of  which  both  sides  are 
willing  to  admit ;  but  while  it  would  seem  that  it 
makes  no  difference  in  the  efficiency  of  a  device 
whether  the  resistances  be  external  to  it,  as  in  the 
rheostat  control,  or  internal,  as  in  the  commutated 
field,  it  is  impossible  to  get  sufficient  resistance 
into  the  field  coils  for  starting  purposes  without 
sacrificing  other  elements  of  efficiency.  Cars 
equipped  on  the  commutated  field  principle  are 
therefore  liable  to  start  with  a  violent  jerk, 
because  even  with  all  the  field  and  armature 
coils  in  series  the  initial  rush  of  current  is  too 
great. 

This  disadvantage  and  the  advantage  possessed 
by  the  rheostat  control  of  permitting  a  perfectly 
gradual  admission  of  current,  together  with  the 
economy  of  current  permitted  by  the  commutated 
field  method,  have  led  to  a  combination  of  the  two 


170  ELECTEIC   RAILWAY   MOTOES. 

being  employed  to  great  advantage.  This  com- 
bination method,  known  as  the  series-parallel 
method  of  control,  is  applicable  where  more  than 
one  motor  is  employed,  and  consists  usually  not  in 
commutating  separate  coils  on  each  field,  but  in 
throwing  the  field  coils  and  the  armature  coils  of 
the  separate  motors  and  various  external  resist- 
ances into  various  combinations  with  each  other. 
It  is  apparent  that  the  greater  the  number  of 
motors  upon  the  car  the  greater  the  flexibility  of 
the  system.  It  therefore  seemed  particularly 
applicable  on  the  Intramural  Railroad  at  the 
World's  Fair,  where  the  motor  car  carried  four 
motors,  and  the  experience  on  that  road  with  the 
system  is  reported  to  have  been  entirely  satisfac- 
tory from  every  point  of  view. 

As  before  stated,  it  has  usually  been  customary 
to  equip  each  car  with  two  motors.  With  this 
arrangement  it  is  often  the  practice  to  cut  one 
motor  out  of  circuit  entirely  when  the  work  re- 
quired is  small.  This  enables  the  remaining 
motor  to  be  operated  at  about  its  most  efficient 
output  on  loads  which  would  be  so  small  as  to 
render  the  operation  of  both  motors  inefficient. 

There  are  many  engineers  who  object  on  theo- 
retical grounds  to  the  use  of  two  motors  under 
any  conditions,  on  account  of  the  tendency  of  any 
two  armatures  to  work  out  of  unison  if  there 
happens  to  be  any  disparity  between  them,  either 
in  the  armatures  themselves  or  in  the  strengths  of 
the  fields  in  which  they  revolve.  It  is  very  evi- 
dent that  if  the  two  motors  fail  to  work  in  the 
most  perfect  unison  the  resultant  effect  will  be 
less  than  it  should.  That  the  perfect  unison  of 
action  between  two  separate  motors,  so  essential  to 
the  highest  efficiency  of  operation,  is  practically 


THE    SPERRY 

unattainable  is,  I  believe,  now  admitted  by  all, 
bat  it  is  approached  so  closely  in  modern  con- 
struction that  this  method  of  equipment,  on  ac- 
count of  the  greater  facility  of  gearing  to  the 
axles  and  the  greater  facility  of  control  by 
coupling  up  armature  and  field  coils  by  the 
series-parallel  method,  is  still  almost  universally 
employed. 

There  are  two  systems  now  on  the  market, 
however,  which  employ  a  single  large  motor 
flexibly  geared  to  both  axles,  and  the  promoters 
of  these  systems  claim  a  largely  increased  tract- 
ive efficiency  for  their  methods  over  that  possible 
with  two  independent  motors.  The  best  known 
of  these  is  the  Sperry  system,  for  which  the  claim 
is  made  that  "  the  motor  being  coupled  to  both, 
axles,  a  tractive  effort  is  available,  which  is 
entirely  impossible  with  separate  motors.  A  per- 
fectly uniform  velocity  of  all  the  wheel  peripheries 
is  obtained  for  adhesive  effect.  The  great  gain  in 
drawbar  pull  under  conditions  of  coupled  axles  as 
compared  with  the  same  torque  applied  to  each 
axle  individually  is  a  matter  not  of  conjecture,  but 
of  fact,  the  difference  being  more  than  eleven  per 
cent.  The  fact  is  that  the  tendency  of  one  wheel 
to  slip  is  held  back  by  all  the  others  instead  of  by 
its  mate  only.  With  separately  driven  axles  one 
pair  may  be  in  slipping  frictional  contact  with  the 
rail  while  the  other  pair  is  doing  the  work  of 
adhesive  contact."  It  is  also  claimed  for  the 
single  motor  system  that  by  substituting  a  large 
single  motor  for  two  small  ones  the  number  of 
wearing  parts  and  consequent  loss  in  friction  is 
greatly  diminished,  the  cost  of  repairs,  inspection 
and  general  care  of  apparatus  materially  lessened, 
and  the  commercial  and  electrical  efficiency  of  the 


172  ELECTEIC    BAIL  WAY   MOTOES. 

system  placed  far  above  that  of  any  double  motor 
equipment. 

While  most  of  these  claims  are  theoretically 
true,  the  mechanical  difficulties  of  gearing  both 
axles  to  the  same  motor  have  been  such  that  the 
theoretical  advantages  of  the  single  motor  have 
not  appealed  to  practical  men  with  sufficient 
force  to  cause  their  general  adoption.  On  the 
contrary,  we  find  to-day  but  one  constructor  build- 
ing motors  with  this  idea  in  view,  whereas  several 
types  of  single  motor  equipment,  once  advertised 
and  pushed  with  considerable  vigor,  have  dis- 
appeared entirety  from  public  view.  Vandepoele, 
Daft,  Eickemeyer,  Rae,  are  names  that  are  all 
connected  with  the  single  motor  equipment 
method,  and  there  are  now  two  more  new  names 
that  must  be  added  to  this  list,  viz.,  E.  H.  John- 
son and  Robt.  Lundell.  These  latter  two  gentle- 
men are  now  before  the  public  with  a  single  motor 
car  equipment  which  seems  to  possess  a  number  of 
features  of  real  merit  not  hitherto  employed.  In 
the  Johnson-Lundell  system  a  single  motor  is 
employed,  but  the  armature  of  this  is  wound  with 
two  independent  sets  of  coils,  each  of  which  has 
its  own  separate  commutator.  There  are  thus 
practically  two  armatures,  but  since  they  are  both 
revolving  in  the  same  field,  they  are  bound  to 
work  in  harmony  if  the  coils  of  the  two  are 
exactly  similar.  This  system  also  permits  of  con- 
trol by  the  series-parallel  method  by  the  handling 
of  the  two  windings  as  though  they  were  separate 
armatures — an  advantage  not  possessed  by  any 
other  single  motor  system.  The  successive  steps 
for  increasing  speeds  in  the  Johnson-Lundell  sys- 
tem as  given  to  the  author  by  the  inventors  them- 
selves are  as  follows  : 


THE    JOHNSON-LUNDELL   SYSTEM.  173 

1.  Starting,   external    resistance,    l£   obms,   all 
field  coils  and  both  armature  coils  in  series. 

2.  Same  as  1  with  resistance  cut  out. 

3.  Field  coils  in  series,  armature  coils  in  parallel. 

4.  All  coils  in  parallel. 

To  give  greater  facility  in  starting,  and  to  take 
up  all  instantaneous  strains,  the  armature  in  the 
Johnson-Lundell  system  is  flexibly  attached  to  its 
shaft  by  means  of  springs  which  permit  a  con- 
siderable angular  motion  of  the  armature  in  case 
of  suddenly  applied  strains  before  the  cushioning 
is  suificient  to  cause  the  revolution  of  the  shaft. 
Besides  permitting  of  a  more  gradual  start  of  the 
car,  which  is  effected  without  jar,  it  is  claimed 
for  this  arrangement  that  it  results  in  economy 
of  current  in  that  it  permits  of  the  generation  of 
some  counter  electromotive  force  at  the  moment 
of  starting,  when  of  all  times  it  is  most  needed 
and  when  in  other  arrangements  it  is  totally 
absent. 

Another  novel  feature  of  this  equipment  is  the 
friction  clutch  arrangement  on  the  armature  shaft. 
Keyed  to  the  latter  is  an  iron  disk  and  pressing 
against  this  are  two  other  similar  disks,  which  are 
forced  against  the  keyed  disc  by  means  of  a  nut 
and  spring  under  compression.  To  these  latter 
discs  are  rigidly  attached  the  two  driving  gears, 
which  in  this  case  are  sprocket  wheels.  By 
tightening  or  loosening  this  nut  a  greater  or  less 
friction  is  maintained  between  the  three  disks.  If 
the  strain  upon  the  motor  exceeds  this  friction 
limit,  the  keyed  disk  will  slip,  allowing  the  arma- 
ture to  continue  to  revolve  instead  of  stopping  it 
suddenly,  as  would  otherwise  be  the  case.  In 
practice  this  friction  is  determined  by  the  maxi- 
mum current  it  is  deemed  wise  to  permit  the 


174  ELECTRIC    RAILWAY   MOTORS. 

armature  to  take.  This  having  been  decided,  the 
compression  of  the  spring  is  adjusted  by  the  nut 
so  that  the  friction  is  just  sufficient  to  permit  the 
inner  disk  to  slip  when  the  dangerous  current  is 
passing  through  the  armature. 

As  before  indicated,  the  car  axles  are  driven 
from  the  motor  shaft  by  means  of  chain  and 
sprocket  gears.  Whether  this  will  prove  entirely 
satisfactory  or  not  in  practice  remains  to  be  seen. 
The  chain  and  sprocket  have  been  repeatedly  tried 
before  on  s-treet  cars,  and  have  been  abandoned  as 
not  suitable — the  chief  difficulty  having  been  the 
rapid  wear  and  breakage  occasioned  by  the  sudden 
strains  to  which  they  were  necessarily  subjected. 
When  in  good  order,  however,  this  method  of 
gear  is  fairly  satisfactory  on  the  score  of  efficiency, 
and  with  the  improvements  introduced  in  the 
Johnson-Lundell  equipment  for  obviating  these 
sudden  strains  and  shocks,  and  with  the  improve- 
ment in  the  chain  gearing  itself,  the  chain  and 
sprocket  may  again  come  into  favor.  It  is  certainly 
the  most  convenient  method  for  gearing  to  both 
axles  from  a  single  motor. 

The  Johnson-Lundell  system  calls  for  special  at- 
tention for  another  reason,  viz.,  that  it  is  the  latest 
attempt  to  do  away  with  the  overhead  trolley.  It 
is  not,  however,  a  conduit  system,  but  rather  a 
surface  contact  system,  the  current  supply  for  the 
motor  being  taken  from  a  surface  conductor  lying 
midway  between  the  rails  and  flush  with  the  street 
paving.  This  conductor  is  not  electrically  con- 
tinuous, however,  but  broken  up  into  lengths  not 
exceeding  eight  or  ten  feet,  which  are  successively 
thrown  into  electrical  connection  with  the  feeder 
system  as  the  car  passes  over  them,  and  discon- 
nected again  after  the  car  passes  off  of  them.  The 


THE   JOHNSON-LUNDELL   SYSTEM.  175 

switching  is  automatically  accomplished  by  elec- 
tromagnetic devices,  one  of  which  is  provided  for 
each  separate  section  of  the  trolley  rail.  These 
switches  are  contained  in  hermetically  sealed  boxes, 
usually  three  in  a  box,  buried  in  the  street  beside 
the  tracks.  On  board  the  car  is  placed  a  storage 
battery  which  is  kept  continually  charged  by  the 
line  current.  The  function  of  this  battery  is  two- 
fold :  first,  to  furnish  the  current  on  starting  the 
car  nedessary  to  actuate  the  electromagnetic  switch 
by  which  the  feeder  current  is  diverted  into  the 
trolley  rail  section  immediately  below  the  car,  and 
second,  to  render  the  car  independent  of  the  power 
station  should  occasion  require,  as  in  case  it  should 
run  off  the  track,  or  where  it  is  required  to  run  the 
car  over  insulated  portions  of  the  track  too  long 
to  be  conveniently  passed  by  the  car's  momentum. 
Since  for  either  use  but  little  drain  is  made  upon 
the  battery,  the  cells  are  not  required  to  be  of  large 
capacity,  and  only  a  sufficient  number  is  required 
so  that  when  coupled  in  series  their  combined 
electromotive  force  will  equal  that  of  the  feeder 
circuit.  On  the  experimental  track  now  in  opera- 
tion in  New  York  the  electromotive  force  of  the 
feeder  current  is  about.  250  volts  ;  100  cells  of  the 
chloride  battery  are  therefore  used.  These  are 
arranged  in  series  under  the  car  seats,  the  whole 
being  in  parallel  with  the  motor  circuit.  When- 
ever their  electromotive  force  falls  below  that  of 
the  trolley  circuit,  a  portion  of  current  from  the 
latter  goes  to  recharge  them.  On  the  other  hand, 
should  the  trolley  circuit  electromotive  force 
drop  they  would  come  temporarily  to  the  latter's 
assistance. 

There  is  still  another  new  system  for  electric 
railways  that  is  destined  to  come  into  prominence 


176  ELECTRIC   RAILWAY   MOTORS. 

in  the  near  future,  viz.,  that  devised  by  Mr.  H. 
Ward  Leonard.  This  system  is  already  in  success- 
ful use  both  on  electric  cranes  and  on  elevators, 
and  in  these  applications  has  demonstrated  its 
great  economy  over  all  other  systems  of  control. 
It  has  been  seriously  objected  to  for  street  car 
application  on  account  of  the  multiplicity  of 
machines  required,  and  has  been  unjustly  con- 
demned because  it  has  been  supposed  that  it  would 
involve  excessive  sparking,  with  sudden  changes  of 
load  or  speed.  As  a  matter  of  fact,  however,  the 
machines  do  not  spark  at  all,  and  the  efficiency  of 
control  is  far  greater  than  is  possible  even  with 
the  series-parallel  method. 


CHAPTER  XX. 

THE   LEONARD,    PERRY    AND   OTHER    SYSTEMS. 

As  before  outlined,  in  speed  regulation  it  is 
necessary  to  vary  the  electromotive  force  as  the 
speed,  and  the  current  as  the  torque  or  effort.  In 
the  previous  methods  of  control  this  is  attempted, 
and  imperfectly  accomplished  by  various  methods 
of  commutation  of  field  coils  and  external  resist- 
ances. In  fact,  some  such  method  as  this  is  all  that 
is  available  where  a  current  of  constant  potential, 
such  as  that  now  universally  employed  on  electric 
railroads,  is  used.  Mr.  H.  Ward  Leonard,  however, 
has  taken  a  very  bold  step  in  his  system,  which 
consists  in  placing  on  each  car  a  separate  generator 
from  which  the  car  motor  is  directly  operated — 
the  generator  itself  being  directly  driven  from  the 
trolley  current  by  a  motor.  By  reference  to  Fig. 
60  the  following  explanation  of  the  system  will  be 
readily  understood.  We  quote  from  a  paper  read 
by  Mr.  Leonard  before  the  American  Institute  of 
Electrical  Engineers,  June  8,  1892: 

"  Each  axle  is  driven  by  a  gearless  motor,  either 
directly  or  by  means  of  a  connecting  rod.  The 
fields  of  these  motors  are  excited  directly  from  the 
constant  E.  M.  F.  of  the  line  and  independently  of 
the  armature  circuit.  Beneath  the  car  and  between 
the  axles  there  is  suspended  a  motor  generator, 
each  armature  winding  being  in  a  separate  field. 
The  motor  portion  of  the  motor  generator  is  shunt 

177 


178 


ELECTRIC   RAILWAY   MOTOES. 


wound  and  connected  just  as  a  shunt  motor  is  for 
use  upon  ordinary  constant  potential  circuits.  The 
field  of  the  generator  portion  has  its  field  connected 
across  the  line,  and  has  inserted  in  it  a  regulating 
and  reversing  field  rheostat.  This  field  circuit  is 
independent  of  the  armature  circuit.  The  gener- 
ating armature  of  the  motor  generator  is  in  metallic 
connection  with  the  armatures  of  the  gearless  pro- 
pelling motors.  It  will  be  noticed  that  this  circuit, 


FIG. 


LEONARD  SYSTEM. 


T,  trolley.  M,  motor  portion  of  power  converter.  G,  generator 
portion  of  power  converter.  P,  the  propelling  motor  for  the  car.  R, 
the  regulation  and  reversing  rheostat  in  field  of  G.  E,  the  connection 
to  ground.  W,  the  car  wheel. 

including  the  armature,  is  a  distinct  and  separate 
metallic  circuit  having  no  connection  with  the  line 
in  any  way. 

"  Suppose  now  that  our  shunt  motor  is  running 
at  full  speed,  and  that  our  controlling  rheostat  in 
the  generator  field  circuit  is  at  its  central  position, 
so  that  the  generator  field  circuit  is  broken. 
Although  the  generator  armature  is  being  driven 
at  full  speed,  it  is  revolving  in  a  field  having  no 
magnetism  except  the  residual  magnetism,  and 


THE    LEONABD   SYSTEM.  179 

hence  produces  practically  no  volts.  Let  us  now 
move  our  controlling  switch  so  as  to  place  the 
generator  field  across  the  line,  but  with  a  resistance 
in  series  with  the  field  of  ten  times  the  resistance 
of  the  field  coils.  We  now  give  a  slight  excitation 
of  the  field  and  a  development  of  volts  at  the  brushes 
of  perhaps  forty  volts.  This  voltage  will  produce 
a  current  through  the  armatures  of  the  driving 
motors  dependent  upon  the  ohmic  resistance  of  this 
circuit  only  ;  and  hence,  even  at  this  low  voltage, 
a  large  current  will  be  produced,  which,  being  in  a 
field  of  full  strength,  will  cause  a  torque  sufficient 
to  start  the  armature.  The  speed  of  the  armature 
will,  of  course,  be  governed  by  the  counter  E.  M.  F. 
which  its  revolution  produces  in  its  strong  field; 
and  hence,  just  as  in  the  case  of  a  shunt  wound 
motor,  its  speed  will  be  practically  constant  so  long 
as  the  E.  M.  F.  supplied  is  constant. 

"If  we  now  gradually  increase  the  magnetic  field 
of  the  generator  by  cutting  out  resistance'by  moving 
the  controlling  switch,  we  will  gradually  raise  the 
E.  M.  F.  of  the  armature  circuit,  and  with  it  the 
speed  of  the  driving  motors.  Since  these  armatures 
are  revolving  in  a  constant  field,  the  torque  they 
produce  will  be  exactly  proportional  to  the  current 
in  them,  and  the  current  will  automatically  flow 
exactly  as  is  required  to  produce  the  necessary 
torque  to  maintain  a  speed  such  that  the  counter 
E.  M.  F.  will  approximately  equal  the  E.  M.  F.  sup- 
plied by  the  power  converter.  Thus  it  will  be  seen 
that  the  speed  of  the  car  will  be  dependent  upon, 
and  proportional  to,  the  E.  M.  F.  supplied  by  the 
power  converter,  and  the  torque  or  tractive  effort 
will  be  dependent  upon,  and  proportional  to,  the 
current  supplied  by  the  power  converter." 

While  this  method  has  not  as  yet  been  actually 


180  ELECTEIC    RAILWAY    MOTORS. 

introduced  on  electric  street  railroads,  its  feasi- 
bility and  economy  and  the  facility  of  control 
afforded  have  been  amply  demonstrated  on  numer- 
ous electric  cranes,  elevators  and  hoists,  and  in 
connection  with  machinery  of  various  kinds  requir- 
ing the  greatest  nicety  of  speed  control  under 
widely  varying  loads.  In  such  applications  econ- 
omy of  space  has  not  been  the  prime  requisite  that 
it  is  in  street  car  traction,  and  the  fact  that  the 
arrangement  seems  necessarily  bulky,  with  the 
three  machines  involved,  and  the  erroneous  idea 
which  has  been  general  that  the  sparking  would  be 
excessive  under  working  conditions,  has  militated 
greatly  against  its  introduction  in  street  railway 
work.  As  before  stated,  those  who  have  examined 
into  the  workings  of  the  system,  among  whom 
may  be  included  the  author,  aver  that  there  is 
practically  no  sparking  even  under  the  most  favor- 
able conditions  for  the  same,  and  the  author  is 
advised  that  changes  in  detail  (though  not  in 
principle)  have  already  been  partially  perfected 
which  will  obviate  the  real  difficulty  that  now 
exists,  viz.,  bulkiness. 

Mr.  Leonard  has  also  adapted  this  same  system 
to  the  operation  of  cars  from  alternating  current 
.circuits.  In  this  application  a  synchronous  motor 
generator  is  substituted  for  the  direct  current 
motor  generator  employed  in  the  direct  current 
method.  Those  who  wish  to  read  a  full  descrip- 
tion of  this  system  are  referred  to  vol.  xi.  of  the 
Transactions  of  the  American  Institute  of  Elec- 
trical Engineers  under  the  title  "  How  shall 
we  Operate  an  Electric  Railway  extending  One 
Hundred  Miles  from  the  Power  Station?"  by 
H.  Ward  Leonard. 


THE    PERKY    SYSTEM.  181 

THE    PERRY   SYSTEM    OF   SERIES    ELECTRIC 
TRACTION. 

Thus  far  the  method  of  distributing  current  for 
electric  traction  has  been  that  by  constant  poten- 
tial. That  is  to  say,  the  pressure  at  the  dynamo 
terminals  has  remained  constant,  and  the  current  in 
amperes  delivered  to  the  moving  cars  has  varied 
as  the  requirements.  This  method  as  a  whole  has 
thus  far  proved  the  most  flexible,  but  with  the  in- 
creasing distances  to  which  our  electric  roads  are 
constantly  reaching  it  is  becoming  less  and  less 
satisfactory.  We  have  already  adverted  to  the 
drop  in  potential  at  the  further  end  of  the  line 
where  the  current  is  used  by  the  present  methods. 
This  drop  can  be  obviated  in  either  of  two  wa}rs, 
either  by  placing  sufficient  copper  in  the  feeders  to 
reduce  it  to  a  bearable  amount,  or  by  increasing 
the  potential.  If  the  potential  be  raised  sufficiently 
to  operate  a  car  properly  at  the  further  end  of  a 
long  line,  it  will  be  too  high  for  the  same  car  when 
nearer  the  power  station,  so  recourse  is  had  to 
additional  copper.  But  the  amount  of  copper  that 
can  be  thus  used  with  an  initial  pressure  of  five 
hundred  volts  is  soon  limited  by  commercial  con- 
siderations, beyond  which  it  becomes  more  expen- 
sive than  to  erect  and  operate  another  power  station 
at  a  distant  point.  Just  how  far  it  is  profitable  to 
operate  a  road  from  a  single  station  must  be 
decided  for  each  particular  case,  but  it  is  probably 
within  the  truth  to  say  that  where  the  distance  to 
be  reached  exceeds  six  or  seven  miles  it  will  be 
cheaper  to  build  a  second  power  house  than  to  put 
sufficient  copper  in  the  feeders  to  render  those 
greater  distances  practicable.  In  the  constant 
potential  method  of  distribution  the  varying 


182  ELECTRIC    RAILWAY    MOTORS. 

demands  for  energy  are  met  by  a  varying  quantity 
of  current,  yet  our  conductors,  which  are  fixed  in 
size,  are  properly  proportioned  only  for  a  given 
current.  For  that  particular  current  they  are  of 
exactly  the  proper  size  ;  but  for  any  other  current, 
be  it  larger  or  smaller,  the  conductor  used  is  not 
the  most  economical  ;  it  will  contain  either  more 
copper  or  less  than  that  which  can  most  econom- 
ically carry  it.  If,  however,  we  should  use  a  con- 
stant current,  and  vary  the  energy  transmitted  by 
varying  the  electromotive  force,  we  could  propor- 
tion our  copper  to  that  current  once  for  all,  and 
since  by  the  conditions  imposed  the  current  does 
not  vary  in  quantity,  the  size  of  our  conductors 
need  not  vary  whatever  the  amount  of  energy  they 
are  required  to  carry  or  whatever  the  distances  to 
be  reached.  Illustrations  of  this  method  of  distri- 
bution are  seen  in  our  arc  light  circuits.  Many  of 
these  already  extend  upward  of  20  miles  and  carry 
from  60  to  100  or  more  2000  C.  P.  lamps,  yet  the 
conductors  on  such  circuits  are  no  heavier  than 
would  be  necessary  for  a  circuit  1  mile  or  5  miles  in 
length  carrying  but  a  single  lamp  or  4  or  5.  To 
render  the  same  sized  conductor  equally  econom- 
ical for  the  transmission  of  large  amounts  of  energy 
to  long  distances,  it  is  only  necessary  to  raise 
the  electromotive  force  correspondingly.  Large 
amounts  of  energy  can  thus  be  much  more  econom- 
ically transmitted  to  long  distances  by  the  constant 
current  method  than  by  the  constant  potential 
method,  the  economy  becoming  particularly  con- 
spicuous where  the  demands  are  variable  and  where 
the  distances  are  also  variable,  as  is  pre-eminently 
the  case  in  electric  traction. 

On  account  of  these  and  other  advantages   of 
the  constant  current  method  of  distribution  many 


THE    PERKY    SYSTEM.  183 

attempts  have  been  made  to  adapt  it  to  street  rail- 
way purposes.  But  there  have  been  difficulties  in 
the  way  of  its  adaptation  to  this  use  which  until 
they  were  removed  introduced  greater  objections 
than  were  the  benefits  sought  to  introduce.  The 
writer,  however,  has  invented  a  system  which  he 
believes  obviates  all  the  difficulties  (see  Trans.  Am. 
Inst.  Elect.  Engineers  for  1892)  hitherto  thought 
to  be  inherent  in  the  constant  current  method,  and 
which  at  the  same  time  sacrifices  none  of  the 
advantages  sought  to  be  gained.  His  improve- 
ment over  previous  methods  consists  simply  in 
supplying  to  the  railway  circuit  the  same  device 
by  which  the  series  arc  light  system  was  con- 
verted from  a  failure  to  a  commercial  success, 
viz.,  an  automatic  cut-out  by  which  on  the  failure 
of  an  operating  device  it  is  automatically  cut  out 
of  circuit.  Without  this  invention  the  practica- 
bility of  even  two  or  three  arc  lamps  in  series  was 
uncertain  ;  with  it  any  number  may  be  practically 
operated. 

Professor  S.  H.  Short  experimented  quite  exten- 
sively a  few  years  ago  with  the  constant  current 
method  of  distribution  for  street  cars,  and  had  for 
a  time  two  roads  in  more  or  less  successful  opera- 
tion —  one,  about  three  miles  in  length,  between 
Huntingtou,  W.  Va.,  and  Guyandotte,  and  the 
other,  of  about  the  same  length,  in  the  city  of  St. 
Louis.  He  had  not  conceived  the  idea  of  the 
automatic  cut-out,  and  found  it  impracticable  to 
operate  more  than  three  cars  simultaneously  on 
his  lines.  He,  however,  demonstrated  the  econ- 
omy and  efficiency  of  the  system  up  to  its  practi- 
cal limit.  With  the  addition  of  the  cut-outs  and 
the  other  radical  changes  introduced  by  the  writer 
it  is  believe^  that  the  new  system  possesses  all  the 


XJHIVERSITY 


184  ELECTRIC   RAILWAY   MOTORS. 

flexibility  of  the  multiple  arc  method  with  the 
additional  advantages  of  the  series  method,  and 
in  recognition  of  these  claims  the  Franklin  Insti- 
tute of  Philadelphia  recently  awarded  him  the 
John  Scott  legacy  premium  and  medal. 

This  system  may  be  briefly  described  as  a 
double  trolley  system,  divided  up  into  sections  of 
greater  or  less  length,  according  to  the  headway  of 
the  cars  provided  for.  Each  of  these  sections  is 
fed  independently  from  a  common  feeder  wire  by 
means  of  electromagnetic  devices  inclosed  in 
hermetically  sealed  boxes  along  the  side  of  the 
track  very  similar  in  design  to  those  employed  in 
the  Johnson-Lundell  system  described  above. 
They  are  not  nearly  so  numerous,  however,  as  in 
the  suburban  districts,  where  the  distances  between 
cars  is  great,  not  more  than  one  or  two  to  the 
mile  are  required.  In  the  cities,  however,  where 
the  headway  of  cars  is  much  less,  their  number 
must  be  increased  proportionately. 

But  one  car  can  operate  on  a  section.  If  a  car 
runs  onto  a  section  already  occupied,  both  cars 
will  become  inoperative  until  one  of  the  two  pulls 
down  its  trolley — thus  constituting  this  a  perfect 
automatic  block  system.  All  cars  on  the  system 
are  in  series  with  each  other,  and  since  the  current 
strength  by  which  they  are  operated  is  invariable, 
their  speed  may  be  checked  on  descending  a  grade 
or  in  bringing  them  to  rest  by  reversing  the  con- 
nections. This  reversal  of  the  brushes  converts 
the  motor  into  a  dynamo,  which,  being  in  series 
with  the  one  at  the  power  house,  contributes  energy 
to  the  line  to  the  last  turn  of  the  wheels.  In  this 
way  the  energy  absorbed  in  ascending  grades  or 
in  starting  from  rest  is  thrown  back  on  the  line 
for  use  elsewhere,  instead  of  being  frittered  away 


STORAGE    BATTERY   TRACTION.  185 

in  heat  on  the  brake  shoe,  as  in  present  methods. 
The  method  of  control  of  cars  operated  by  this 
system  is  ideally  simple.  There  are  neither  corn- 
mutated  fields  nor  external  resistances  to  be  con- 
sidered, so  that  with  this  system  the  advocates  of 
both  methods  of  control  join  hands,  since  the 
method  involves  the  disadvantages  of  neither.  In 
the  series  system  the  car  is  started,  speeded  up, 
slowed  down  and  reversed  by  simply  shifting  the 
position  of  the  brushes  on  the  commutator.  The 
equipment  of  the  generating  or  power  station  is 
also  extremely  simple,  requiring  for  each  unit 
nothing  more  than  a  voltmeter,  an  ammeter  and  a 
line  switch  by  which  the  circuit  can  be  closed  or 
opened,  no  rheostats,  bus  bars  or  complicated 
switchboard  systems  being  required.  This  system 
is  thought  to  be  peculiarly  applicable  to  long  lines, 
such  as  suburban  and  interurban  lines,  and  it  is 
believed  that  the  time  is  not  far  distant  when  its 
advantages  on  such  lines  will  be  fully  appreciated. 

STORAGE    BATTERY   TRACTION. 

A  self-contained  car  or  one  that  is  self-propel- 
ling would  be  an  ideal  were  there  not  attendant 
disadvantages  of  such  a  serious  nature  as  to  over- 
shadow the  advantages  possessed.  The  storage 
battery  seemed  to  hold  out  such  bright  prospects 
of  success  that  many  earnest  efforts  have  been 
made  almost  from  the  first  invention  of  the  stor- 
age battery  by  Plante  and  its  improvement  by 
Faure  down  to  the  present  day.  It,  however,  has 
been  a  disappointment  in  every  case,  in  this  coun- 
try at  least,  where  it  has  been  tried,  notwithstand- 
ing the  fact  that  neither  engineering  skill  of  the 
highest  character  nor  expense  has  been  spared  to 


186  ELECTRIC   RAILWAY   MOTORS. 

make  it  a  success.  The  causes  of  these  failures 
are  many  and  seem  to  be  inherent  in  the  battery 
itself  as  at  present  constructed.  We  know  of  no 
more  efficient  method  of  storing  electricity  *  than 
by  means  of  lead  plates.  These  are  so  heavy  that 
a  street  car  equipped  with  sufficient  battery  capac- 
ity for  its  successful  propulsion  must  carry  in  this 
form  alone  more  weight  than  it  is  possible  to  put 
upon  it  in  the  shape  of  passengers.  The  empty 
car  is  therefore  handicapped  on  starting  out  with 
a  non-paying  load  greater  than  that  from  which 
it  can  expect  to  derive  revenue.  This  means  not 
only  additional  expense  for  haulage,  but  is  destruc- 
tive to  track  and  cars  alike.  Since  at  least  two 
sets  of  battery  equipments  must  be  provided  for 
each  car,  which  will  greatly  exceed  the  cost  of 
motor  equipment,  the  fixed  capital  investment 
upon  which  interest  must  be  earned  is  excessive. 
Another  disadvantage  of  the  battery  is  that  not 
more  than  about  seventy  per  cent,  of  the  energy 
put  into  it  can  be  drawn  out  of  it  again  for 
use,  and  even  this  amount  is  available  only  when 
the  batteries  are  new  and  in  good  condition. 
When  they  are  old,  the  percentage  of  energy  used 
for  charging  that  is  available  for  use  is  very  much 
less  than  this,  running  down  to  fifty,  forty,  thirty 
per  cent.,  and  even  less.  The  deterioration  of  the 
plates,  too,  is  very  rapid  in  street  car  work  owing 
to  the  jarring  of  the  cars  and  the  swash  of  the 
liquid,  causing  a  loosening  of  the  active  material, 
its  falling  out  and  causing  short  circuits,  resulting 

*  It  is  not  electrical  energy  that  is  stored  in  the  storage 
battery,  as  is  popularly  assumed,  but  chemical  energy.  The 
term  "  electrical  storage  "  has  come  into  such  general  use, 
however,  and  it  is  so  convenient,  that  with  this  explanation 
I  may  use  it  without  creating  confusion. 


CONDUIT   SYSTEMS.  187 

in  the  destruction  of  the  plates.  The  wear  and 
tear  or  depreciation  account  is,  therefore,  excessive, 
and,  taken  altogether,  experience  has  almost  con- 
clusively pointed  to  the  inadaptability  of  the  stor- 
age battery  to  traction  purposes. 

The  storage  battery,  however,  permits  of  the 
most  economical  speed  control  of  any  known,  as  by 
commutating  the  cells  into  groups  in  series  and  in 
parallel,  by  using  some  for  separately  exciting  the 
fields,  while  various  other  combinations  are  used 
for  feeding  the  armature,  an  ideally  economical 
speed  regulation  is  obtained,  somewhat  similar  to 
that  advocated  by  Mr.  Leonard,  but  without  the 
multiplicity  of  apparatus  or  external  resistances 
used  by  him. 

Should  a  lighter  and  more  durable  storage  bat- 
tery than  the  present  type  ever  be  invented  it  is 
not  unlikely  that  it  would  come  into  general  use 
for  traction  purposes,  but  with  our  present  types 
it  seems  exceedingly  unlikely  that  it  can  make 
much  progress  in  this  direction. 

CONDUIT    SYSTEMS. 

The  unsightliness  of  the  overhead  trolley  and 
its  obtrusiveness  in  the  streets  are  its  chief  objec- 
tionable features.  To  overcome  these  many  at- 
tempts have  been  made  to  carry  the  wire  under- 
ground in  a  conduit  similar  to  that  used  in  cable 
railways.  It  would  seem,  at  first  blush,  a  very 
simple  thing  to  place  the  trolley  wire  in  such  a 
conduit  and  have  it  work  at  least  as  well  as  it  does 
overhead,  for  that  is  all  that  is  asked  of  any  con- 
duit system,  but  difficulties  have  arisen  that  have 
militated  against  the  success  of  the  conduit  sys- 
tem thus  far  that  have  brought  it  into  disfavor. 


188  ELECTRIC    RAILWAY   MOTORS. 

The  chief  difficulty,  to  my  own  mind,  is  the  greater 
expense  involved  in  such  a  plant.  It  is  but  nat- 
ural that  parties  having  railway  franchises  should 
desire  to  avail  themselves  of  them  by  the  least 
expensive  and  most  efficient  means  where  those 
two  qualities  are  not  incompatible.  It  so  happens 
that  the  overhead  trolley  does  possess  both  of  these 
qualities,  hence  since  there  is  no  advantage  to  the 
investor  in  putting  the  trolley  wire  below  the  sur- 
face of  the  street,  but,  on  the  contrary,  a  disadvan- 
tage in  the  way  of  greater  expense,  capital  has 
not  had  the  incentive  to  investment  in  conduit 
systems  that  have  been  offered  by  the  overhead 
trolley.  In  our  larger  cities,  however,  the  public 
is  already  clamoring  for  the  burial  of  the  wires, 
and  with  this  incentive  many  inventors  are  at 
work  endeavoring  to  devise  a  practicable  conduit 
system  which  shall  not  at  the  same  time  be  too 
expensive  either  in  installation  or  in  operation. 

The  chief  difficulties  to  be  overcome  in  conduit 
work  are  to  maintain  an  efficient  insulation  of  the 
trolley  wires  from  the  ground  or  conduit  itself  ;  to 
prevent  the  insulation  of  the  trolley  wire  from 
the  trolley  contact  by  dirt  entering  through  the 
slot  ;  from  mechanical  and  electrical  difficulties, 
switches,  etc. ;  and  to  provide  an  efficient  contact 
between  trolley  and  wire  under  conditions  which 
prevent  the  entrance  of  dirt  into  the  slot. 

The  two  best  known  examples  of  successful 
conduit  construction  are  the  Siemens  and  Halske 
and  the  Love  systems,  in  both  of  which  the  prin- 
ciple of  the  overhead  trolley  is  followed  closely. 
The  conductors,  however,  are  not  placed  directly 
beneath  the  slot,  but  off  to  one  side,  where  they  are 
protected  by  the  roof  of  the  conduit  from  in-fall- 
ing dirt,  water  or  snow.  The  traveling  contacts 


CONDUIT   SYSTEMS.  189 

are  made  of  proper  shape  to  reach  around  to  the 
conductors,  with  which  they  are  brought  into  con- 
tact when  desired.  In  the  Siemens  and  Halske 
system,  which  has  now  been  in  successful  opera- 
tion for  several  years  abroad,  the  conduit  and  slot 
are  at  the  side  of  the  track.  In  the  Love  system, 
which  has  been  tried  in  Chicago  and  is  now  in 
successful  operation  in  Washington,  the  conduit  is 
in  the  center  of  the  track.  While  these  two  sys- 
tems differ  considerably  in  details,  they  are  the 
same  in  principle,  whicli  is  exactly  that  of  the 
overhead  trolley,  special  attention  being  given  to 
the  insulation  of  the  trolley  wire  from  its  sur- 
roundings, to  the  adequate  drainage  of  the  conduit 
itself  and  to  adapting  the  trolley  to  its  new 
requirements. 

Other  inventors  liave  endeavored  to  solve  the 
insulation  problem  somewhat  on  the  same  lines 
as  those  adopted  in  the  surface  contact  system  of 
Johnson  and  Lundell,  namely,  by  dividing  the 
trolley  wire  up  into  short  sections  which  are  nor- 
mally dead,  but  which  are  successively  thrown 
into  electrical  connection  with  the  live  feeder  wires 
as  the  trolley  passes  onto  them,  and  thrown  out  of 
connection  with  them  as  the  trolley  passes  off 
from  them.  By  thus  having  only  that  portion  of 
the  trolley  wire  actually  in  use  active,  the  tendency 
to  leakage  of  current  is  of  course  greatly  lessened, 
but  there  is  introduced  in  its  stead  a  multiplic- 
ity of  switches  upon  whose  proper  working  the 
success  of  the  system  depends,  which  is  of 
course  a  source  of  weakness,  or  possible  weak- 
ness, scarcely  less  desirable  of  avoidance  than 
leakage  itself.  Great  ingenuity  has  been  dis- 
played in  designing  systems  on  this  plan,  but  none 
of  them  has  been  in  practical  use  long  enough 


190  ELECTRIC    BAIL  WAT   MOTORS. 

to  demonstrate  beyond  question  its  absolute  practi- 
cability. 

Still  another  type  of  conduit  known  as  the 
closed  conduit  has  been  devised  in  which  by  vari- 
ous means,  usually  by  electromagnetic  devices, 
the  passing  car  maintains  a  supply  of  current  by 
attracting  to  short  surface  conductors  the  live 
conductors  buried  beneath  the  surface  of  the 
street.  Sometimes  this  contact  is  made  by  the 
pressure  of  the  car  wheels  or  their  flanges  upon 
spring  contacts  over  which  they  pass,  but  in  all 
cases  the  methods  of  speed  control  are  identical 
with  those  employed  on  the  overhead  trolley 
systems. 


CHAPTER  XXL 

THE    MANAGEMENT    OF    STEEET    RAILWAY    MOTORS. 

AT  the  outset  of  this  chapter  the  author  might 
as  well  confess  his  inability  to  teach  a  novice,  either 
by  letterpress  or  pen,  how  to  actually  manage  an 
electric  street  car  in  its  various  moods  and  whims, 
if  so  they  may  be  called.  If  he  can  impress  upon 
his  readers  at  the  outset  that  motors  do  not  have 
whims  at  all,  and  that  the  seeming  irregularities 
of  their  behavior  are  all  due  to  definite  causes 
which  are  in  most  cases  within  the  control  of  the 
motor  man,  he  will  have  made  a  good  start.  No 
one  from  book  reading  alone  can  expect  to  step 
full-fledged  a  motorman  upon  his  car.  There  is 
much,  after  all  is  told,  that  must  be  learned  by 
actual  experience.  For  instance,  the  sound  of  the 
motors  often  tells  one  much,  and  not  only  indicates 
either  that  everything  is  all  right  and  permits  him 
to  continue  on  with  confidence,  or  that  something 
is  wrong,  and,  moreover,  frequently  indicates  just 
what  is  wrong,  or  so  nearly  so  that  the  experienced 
motorman  need  not  look  far  to  find  the  trouble, 
whereas  the  novice  might  spend  an  hour  or  two 
fruitlessly  hunting  for  the  fault.  And  this  was 
the  moral  intended  to  be  taught  by  the  little 
anecdote  at  the  beginning  of  this  book. 

We  believe,  however,  that  if  one  thoroughly 
understands  the  construction  of  his  apparatus  and 
the  principles  upon  which  it  operates,  the  instruc- 

191 


192  ELECTEIC    RAILWAY   MOTOBS. 

tions  which  follow  will  well  supplement  a  grow- 
ing experience,  and  enable  the  conscientious 
operator  to  avoid  many  difficulties,  and  to  correct 
them,  when  they  do  occur,  the  more  readily.  It 
was  with  the  object  of  leading  up  to  the  manage- 
ment of  the  motor  rather  than  of  teaching  it  that 
this  work  has  been  undertaken.  It  only  remains  for 
us  to  give  a  little  kindly  advice,  which  it  is  hoped 
the  reader  will  by  this  time  have  been  prepared  to 
understand.  The  remaining  pages  will  therefore 
partake  more  of  the  nature  of  those  medical  works 
intended  for  family  use  than  of  the  nature  of  a 
technical  medical  treatise. 

The  first  thing  to  keep  in  mind  is  to  keep  your 
motor  dry,  for  if  it  get  wet  the  whole  structure  is 
liable  to  give  way — burn  out.  The  second  word  of 
advice  is  to  keep  it  clean,  for  thereby  most  of  its 
ills  will  be  avoided.  Water  and  dirt  are  the  two 
greatest  enemies  of  the  electric  motor.  The  third 
is,  study  the  wiring  of  your  car,  so  that  you  have 
clearly  mapped  out  in  your  mind  the  various  con- 
nections and  their  functions.  This  will  enable 
you  to  test  out  a  fault  which  could  not  easily  be 
detected  by  the  eye,  and  to  locate  it,  at  any  rate, 
within  a  given  circuit.  In  giving  this  last  advice 
to  the  motorman  the  author  is  not  unmindful  of 
the  difficulty,  nay,  even  the  impossibility,  of  the 
motorman's  being  able  to  trace  out  the  wiring  of 
his  car  unassisted.  To  do  this  he  must  have  the 
full  co-operation  of  those  in  authority  ;  and  here 
we  have  a  word  of  advice  to  give  to  those  in  charge 
of  the  rolling  stock. 

If  a  motorman  or  other  employee  of  yours,  hav- 
ing in  the  performance  of  his  duty  to  do  with 
your  motors,  wishes  any  information  in  regard  to 
the  same  which  it  is  in  your  power  to  supply, 


MANAGEMENT    OF   RAILWAY   MOTORS.  193 

supply  it  fully  and  freely.  In  fact,  it  is  your  duty, 
if  you  would  have  good  service,  to  educate  your 
employee  to  the  highest  degree  possible  in  his 
duties.  Do  not  be  content  to  let  him  do  things 
with  your  machinery  simply  because  you  tell  him 
to,  thereby  making  of  him  a  machine  which  is 
even  more  likely  to  get-  out  of  order  than  the 
inanimate  machinery  he  has  to  handle  ;  but  after 
telling  him  what  to  do  and  what  not  to  do  try  to 
explain  to  him  the  reasons  therefor,  and  the  penalty 
— not  to  him,  but  to  the  machinery  in  his  charge — 
of  disobedience.  Encourage  him  to  ask  proper 
questions — and  all  questions  in  regard  to  his 
motors  are  proper  ones — and  help  him  to  become 
an  intelligent  man  ;  for  by  so  doing  alone  can  you 
get  the  best  service,  the  most  for  your  money. 

The  next  advice  to  the  motorman  is  that  he 
study  the  "  habit "  of  his  motors.  Let  him  keep 
his  ears  open  to  every  sound  until  any  variation 
from  the  same  would  awaken  him  even  if  he  were 
asleep,  for  the  sounds  given  out  by  the  motor  are 
as  surely  an  indication  of  its  condition  as  is  the 
pulse  of  a  human  being  of  his  state  of  health.  A 
variation  from  the  normal  sound  is  often  the  first 
indication  the  operator  may  have  of  trouble  with 
his  machines.  If  heeded  at  once,  disaster  ma}r  be 
entirely  averted  where  it  might  otherwise  almost 
surely  follow. 

If  the  ear  detects  anything  unusual,  the  car 
should  be  stopped  at  once  and  a  careful  examina- 
tion made  to  detect  if  possible  the  cause.  If  it 
cannot  be  located  at  once,  it  may  be  well  to  cut  out 
first  one  motor  and  then  the  other,  running  the 
car  carefully  for  a  short  distance  with  each  sepa- 
rately, if  the  grades  are  such  as  to  make  this  safe. 
In  this  way  the  trouble  may  be  located  by  sound 


194  ELECTRIC    RAILWAY   MOTORS. 

in  the  motor  in  which  it  exists,  and  thus  its  specific 
nature  and  exact  location  be  more  easily  traced. 

The  most  common  diseases  of  electric  motors  of 
any  kind,  street  car  motors  included,  their  symp- 
toms and  remedies,  are  the  following  : 

First  of  all  comes 

SPARKING   AT   THE    COMMUTATOR. 

A  properly  constructed  motor  in  normal  work- 
ing condition  should  not  spark  at  all,  or  at  least 
not  noticeably.  Sparking  may  therefore  be  re- 
garded more  as  a  symptom  of  a  disease  than  as 
a  disease.  The  sparking  of  the  commutator  is 
often  the  first  indication  that  the  operator  has  that 
everything  is  not  as  it  should  be.  When  sparking 
is  observed,  therefore,  an  investigation  should  be 
made  at  once  to  determine  its  cause  and  to  rectify 
it  on  the  spot,  if  possible,  or,  in  case  it  is  not  pos- 
sible to  do  this,  to  run  the  car  into  the  shop  for 
repairs.  Sparking  should  be  stopped  for  its  own 
sake,  however,  for  if  allowed  to  continue  it  will 
corrode  the  commutator  blocks,  and  in  this  way 
increase  itself  until  the  commutator  is  so  far  gone 
as  to  require  renewal. 

Crocker  and  Wheeler,  in  their  most  excellent 
little  work  on  "The  Practical  Management  of 
Dynamos  and  Motors,"  assign  fourteen  different 
causes  for  sparking,  not  all  of  which,  however, 
need  concern  us  here.  The  following,  however, 
are  those  which  especially  concern  the  motorman  : 

First  Cause. — Armature  carrying  too  much  cur- 
rent. This  means  that  the  motor  is  being  over- 
worked. The  motorman  need  not  be  alarmed  if 
his  motor  sparks  some  on  ascending  a  heavy  grade, 
for  that  is  rather  to  be  expected,  especially  if  the 


SPARKING   AT   THE    COMMUTATOR.  195 

load  be  at  the  same  time  heavy.  The  remedy  for 
this,  of  course,  is  to  save  your  motor  as  much  as 
possible  by  gaining  momentum  before  reaching  a 
grade,  and  then  maintaining  a  uniform  slow  speed 
until  the  grade  is  passed.  A  motor  that  sparks  on 
ascending  a  grade  should  never  be  stopped  on  the 
grade,  if  it  can  by  any  possibility  be  avoided,  as 
on  starting  again  the  work  it  will  be  called  upon 
to  do  will  be  many  times  that  which  it  ought  to 
do,  and  disastrous  results  may  follow. 

But  the  sparking  from  overload  may  not  always 
be  due  to  the  excessive  useful  work  the  motor  is 
performing.  It  may  be  due  to  the  striking  of  the 
armature  against  the  pole  pieces,  to  the  binding  of 
the  armature  shaft  in  its  bearings,  to  a  bad  short 
circuit  or  to  the  grounding  of  the  motor  on  the 
frame.  Any  of  these  latter  causes,  if  active,  are 
likely  to  cause  sparking  when  the  motor  is  not 
doing  much  apparent  work,  and  this  fact  will  help 
to  distinguish  which  of  the  two  classes  of  troubles 
causes  the  overloading.  The  general  indication 
that  the  sparking  is  due  to  overload  is  the  over- 
heating of  the  whole  armature.  If  this  overload 
is  due  to  frictional  causes,  they  may  be  detected 
by  examination  first  of  the  bearings,  which  will  be 
unusually  hot  if  the  trouble  lies  there,  and  second 
by  an  examination  of  the  armature.  If  friction  is 
indicated  there,  the  trouble  is  extremely  serious, 
as  in  overwound  armatures  (viz.,  those  on  which 
the  coils  are  wound  on  the  surf  ace  as  distinguished 
from  the  iron-clad  armatures,  in  which  the  coils 
are  placed  in  slots  on  the  surface,  and  therefore 
beneath  the  surface)  continued  friction  is  sure  to 
wear  off  the  insulation  and  cause  a  burn-out  of  the 
armature.  In  this  case  the  motor  man  should 
exercise  his  mechanical  ingenuity,  and  so  center 


196  ELECTRIC    RAILWAY    MOTORS. 

his  armature  that  it  will  not  strike  the  fields  at 
all. 

Second  Cause. — Brushes  not  set  at  the  neutral 
point.  We  have  seen  that  there  are  two  positions 
in  every  revolution  of  a  coil  in  which  it  generates 
no  electromotive  force.  In  a  two-pole  machine 
these  two  positions  are  diametrically  opposite  each 
other,  and  in  a  four-pole  machine  they  are  90°  from 
each  other.  These  points  are  called  the  neutral 
points.  If  the  brushes  bear  at  exactly  these  points, 
there  should  be  no  sparking,  but  if  they  bear  at  any 
other  points  on  the  commutator  the  brushes  will 
pass  off  from  bars  that  have  an  electromotive  force 
which  is  greater  the  further  the  brushes  are  re- 
moved from  the  neutral  points,  and  it  is  this  electro- 
motive force  that  causes  the  sparking.  We  have 
seen  that  as  the  current  supplied  to  the  motor 
changes,  so  do  the  positions  of  these  neutral  points 
in  some  machines,  so  that  it  is  necessary  in  such 
to  move  the  brushes  back  and  forth  as  the  load 
varies.  It  is  this  change  of  the  positions  of  the 
neutral  points  that  causes  the  sparking  due  to  over- 
load, just  described.  But  the  ampere  turns  on 
street  railway  motors  on  the  armatures  and  fields 
are  so  disposed,  the  one  predominating  over  the 
other  to  such  an  extent  that  the  load  may  vary 
within  wide  limits  without  perceptible  change  of 
the  neutral  points.  The  brushes  are  therefore 
usually  fixed  once  for  all  at  the  proper  places,  so 
that  the  sparking,  if  due  to  the  brushes,  is  probably 
due  to  one  or  more  of  the  following  causes  rather 
than  to  wrong  position  : 

a.  Commutator  rough,  eccentric  or  has  one  or 
more  high  bars,  or  what  are  termed  fiats.  To  de- 
tect these  the  commutator  should  be  examined 
while  at  rest  for  roughness  and  also  for  eccen- 


SPARKING   AT   THE   COMMUTATOR.  197 

tricity.  This  latter  can  be  detected  better,  how- 
ever, by  watching  the  motor  carefully  when  slowly 
in  motion.  If  the  brushes  alternately  rise  and  fall, 
the  commutator  is  not  centered  properly  on  the 
axle.  When  running  fast,  the  whole  armature 
may  chatter.  High  bars  or  flats — the  latter  being 
flat  surfaces  on  the  commutator — are  best  detected 
while  the  motor  is  running  by  resting  the  finger 
nail  against  the  commutator.  Any  irregularity  of 
surface  will  thus  be  readily  detected.  These  are 
all  difficulties  with  which  the  motorman  would 
better  not  fool,  for  fear  of  increasing  the  trouble. 
His  duty  will  have  been  done  if  he  cuts  out  this 
motor  a'nd  proceeds  to  the  car  barns  at  once  with 
the  other  motor. 

b.  Brushes  make  poor  contact  with  the  com- 
mutator. Close  examination  will  show  that  the 
brushes  touch  only,  at  one  corner  or  only  in  front 
or  behind,  or  there  is  dirt  on  the  surface  of  contact. 
The  remedy  for  this  trouble  readily  suggests  itself. 
Clean  the  commutator  and  replace  the  brushes, 
being  careful  that  they  have  ample  bearing  on  the 
commutator.  Occasionally  the  fault  lies  in  the 
brush  itself :  it  may  be  extremely  hard,  or  have 
extremely  hard  spots  in  it  which  wear  away  less 
readily  than  the  remainder  of  the  carbon.  The 
remedy  for  this  is  to  throw  away  such  brushes  and 
replace  them  by  new  ones. 

Sometimes  a  good  brush  has  worn  unevenly 
through  grit  on  the  commutator,  and  only  needs 
dressing  down  to  give  good  service.  This  is  best 
done  by  drawing  a  strip  of  sandpaper  back  and 
forth  between  it  and  the  commutator  while  the 
brushes  are  pressed  down.  This  will  dress  their 
bearing  surfaces  to  fit  the  commutator  properly. 

Third  Cause. — Short-circuited  coil  in  armature. 


198  ELECTRIC    RAILWAY   MOTORS. 

This  may  be  caused  by  a  little  carbon  dust  or 
other  conducting  material  getting  in  between  two 
of  the  commutator  bars  or  between  the  connections 
leading  to  the  bars.  Perhaps  the  best  indication 
of  a  short-circuited  coil  is  the  increase  of  heat  in 
that  particular  coil  or  coils  on  the  armature.  If 
in  feeling  around  the  surface  of  the  armature  one 
or  more  coils  appear  much  hotter  than  the  rest,  a 
short-circuited  coil  is  to  be  suspected,  and  a  care- 
ful examination  of  the  commutator  and  its  connec- 
tions should  be  made  to  discover  the  cause,  and  if 
found  it  should,  of  course,  be  removed.  If  the 
cause  be  removed  early  in  the  trouble  it  may  have 
done  no  harm,  but  a  short  circuit  is  very  likely  to 
cause  a  burn  out  of  the  armature.  If  the  trouble 
is  in  the  commutator  or  its  connections,  its  remedy, 
if  taken  in  time,  is  exceedingly  simple,  but  the 
short  circuit  may  be  in  the  armature  itself,  and  if 
so  cannot  be  corrected  by  the  motorman.  If  he 
have  reason  to  suspect  that  it  exists  in  the  arma- 
ture, his  only  recourse  is  to  cut  that  motor  out  and 
proceed  to  the  stables  with  the  other  motor.  The 
short-circuited  coils  will  there  have  to  be  replaced 
by  new  ones. 

The  same  effect  may  be  produced  exactly  by  a 
"ground"  on  the  armature,  which  together  with 
the  intentional  ground  forms  a  short  circuit.  The 
indication,  aside  from  the  unduly  heated  coil,  is 
very  bad  sparking  occurring  at  intervals. 

Fourth  Cause. — Broken  circuit  in  armature. 
This  is  usually  indicated  by  violent  flashes  like 
the  preceding,  but  unaccompanied  by  the  heating 
of  the  coil,  the  flashing,  as  before,  occurring  at 
intervals  when  the  commutator  segment  belonging 
to  the  broken  coil  passes  under  the  brushes.  The 
flashing  in  this  case  will  be  very  much  worse  than 


MOTOR   STOPS    OR    FAILS   TO    START.  199 

in  the  preceding  case,  even  when  the  motor  is  run- 
ning slowly.  Examination  should  be  made  to  see 
that  the  flash  is  not  due  to  a  high  bar  or  dirt  or 
other  insulating  material  on  one  of  the  bars.  If 
not  due  to  either  of  these,  the  break  is  most  likely 
to  be  found  in  the  connections  between  the  arma- 
ture coils  and  the  commutator  bars.  If  it  be  due 
to  a  broken  commutator  connection,  a  temporary 
remedy  is  found  in  connecting  the  disconnected 
bar  with  its  neighbors  by  driving  in  between  the 
bars  a  piece  of  copper  wire  so  as  to  short-circuit 
the  broken  coil.  If  the  break  be  in  the  coil  itself, 
rewinding  is  probably  necessary,  and  the  motor 
should  be  cut  out  of  circuit  at  once. 

Fifth  Cause. — Chatter  of  brushes.  The  com- 
mutator sometimes  becomes  sticky  when  carbon 
brushes  are  used,  causing  friction,  which  throws 
the  brushes  into  rapid  vibration.  When  this  is 
the  case,  it  is  readily  detected  by  the  tingling  or 
jarring  sensation  produced  on  the  hand  when 
lightly  placed  on  the  brushes.  At  the  first  oppor- 
tunity the  commutator  should  be  cleaned  with  a 
rag  or  waste  and  oiled  slightly.  This  will  stop  the 
trouble  at  once. 

Sixth  Cause. — Flashing  all  around  the  commuta- 
tor. This  may  be  due  either  to  particles  of  car- 
bon between  the  bars  or  to  broken  coils,  or  both, 
and  the  remedy  is  that  recommended  before  for 
such  troubles.  If,  after  cleaning  the  commutator 
and  no  breaks  are  found,  the  flashing  continues, 
the  motor  should  be  disconnected  and  the  car  run 
into  the  shops  for  overhauling. 

MOTOR    STOPS    OR   FAILS   TO    START. 

First  Cause. — Great  overload. 

Second  Cause. — Very  excessive  friction  due  to 


200  ELECTRIC    RAILWAY   MOTORS. 

shaft,  bearings  or  other  parts  being  jammed,  or 
armature  touching  pole  pieces.  In  either  of  these 
cases  the  armature  would  most  certainly  burn  up 
were  it  not  for  the  fuses,  which  are  intended  to 
melt  and  break  the  circuit  before  sufficient  heat 
can  be  generated  in  the  armature  coils  to  do  dam- 
age. A  careful  examination  should  be  made  to 
see  what  the  trouble  is,  and  it  should  be  rectified, 
if  possible,  at  once. 

Third  Cause. — Circuit  open,  due  to  :  (a)  Safety 
fuse  melted,  (b)  connection  to  motor  broken  or 
slipped  out  of  binding  post,  (c)  brushes  not  in  con- 
tact with  commutator,  (d)  hood  or  canopy  switch 
open,  (e)  broken  or  imperfect  contact  in  control- 
ling rheostat,  (/')  failure  at  generating  station. 
Trouble  due  to  any  of  these  causes  is  indicated  if 
the  car  fails  to  move  when  load  is  removed  or 
when  load  is  light.  In  such  cases  the  current 
should  be  turned  off  immediately  at  the  hood 
switch,  and  the  break  looked  for  as  indicated. 
The  lamp  circuit  should  be  turned  on.  If  lamps 
burn  or  other  cars  are  found  to  be  moving,  the 
trouble  does  not  lie  with  the  generating  station. 


CHAPTER  XXII. 

SPECIFIC    DIRECTIONS    TO    MOTORMEN. 

SOME  of  the  electrical  companies  furnish,  and 
all  of  them  should  furnish,  a  list  of  empirical  rules 
for  the  management  of  their  motors.  It  is  too  often 
that  the  motormen  never  see  these  rules  at  all,  but 
receive  them  by  word  of  mouth  from  the  foremen 
or  whomever  they  look  to  for  instructions.  It  is 
very  desirable  that  each  motorman  should  have 
these  rules  in  convenient  form  for  reference,  and 
they  are  herewith  reproduced.  They  are  essen- 
tially the  same  for  all  makes  of  motors,  and  are  as 
follows  : 

1.  In  taking  a  car  out  of  the  barn  where  it  has 
been  standing  with  trolley  off  put  on  the  trolley, 
place  handles  on  controlling   stand  and  see  that 
the  current  is  off  ;  then  throw  in  the  hood  switch. 

2.  On  most  modern  equipments  there  are  two 
levers — one  for  reversing,  the  other  for  controlling 
the  current  and  speed  of  car.     In  starting  move 
the  controller  Quickly  from  right  to  left  until  you 
feel  the  contact  touch  the  first  point,  and  then 
slowly    move    it    farther    until   the    car    moves. 
Allow  the  car  to  gain  a  little  headway,  and  then 
move  on  as  the  car  gains  headway  till  the  lever  is 
as  far  as  it  will  go.     Usually  the  controller  switch 
should  be  allowed  to  rest  on  each  successive  notch 
long  enough  for  the  car  to  gain  the  headway  due 
to  that  combination  before  it  is  moved  to  the  next 

901 


202  ELECTRIC   RAILWAY    MOTOES. 

notch.  In  the  Westinghouse  control  the  first 
notch  throws  the  whole  resistance  and  the  two 
motors  in  series.  The  second  notch  cuts  out  half 
the  resistance,  and  the  third  notch  the  whole 
resistance.  The' fourth  notch  throws  both  motors 
in  parallel  with  one  another  and  each  in  series 
with  half  the  resistance.  The  fifth  notch  cuts  out 
the  resistance  of  one  motor,  and  the  sixth  or  last 
notch  cuts  out  the  resistance  of  the  other  motor, 
leaving  them  in  parallel,  which  gives  the  greatest 
speed  and  highest  efficiency.  In  this  arrangement, 
which  is  a  series-parallel  arrangement,  the  first 
two  notches  are  merely  starting  points,  and  the 
handle  should  only  be  allowed  to  rest  momentarily 
on  each.  The  third  is  a  good  slow  speed  running 
notch.  To  obtain  greater  speed  or  more  pressure 
the  handle  should  be  moved  slowly,  but  con- 
tinuously, from  the  third  to  the  fourth  notch. 
This  and  the  next  notch  should  be  used  only 
momentarily,  not  steadily.  In  this,  as  with  all 
other  arrangements,  the  last  notch  should  be  used 
for  heavy  work  or  fast  running. 

3.  Before  leaving  the  car  barns,  however,  the 
motorman  should   examine   carefully  the   grease 
cups  and  see  that  they  are  filled.     Examine  brushes 
and  motors,  making  sure  they  are  in  fit  condition 
to  begin  the  day's  work. 

4.  With  hood  switches  open,  try  the  reversing 
lever  and  controller  lever  to  make  sure  they  are  in 
good  working  order.     Then,  with  controller  lever 
off,  close  hood  switches ;  note  that  trolley  is  on 
the  line  and  that  you  have  a  current  by  lamps 
being  lighted.    Now  move  controlling  lever  around 
slowly.     If  car  moves   off,  all  is  probably  right. 
If  car  refuses  to  move  after  controlling  lever  is 
moved  to  last  notch,  turn  lever  back  to   "off" 


UNIVERSITY 

SPECIFIC    DIRECTIONS   T 


point,  get  down  from  car  and  note  that  rail  is 
clean,  that  the  fuse  plug  is  in  place,  that  the  ground 
wire  from  motors  is  attached  to  truck  frame  and 
that  the  cut-out  switches  for  both  motors  are 
closed.  If  the  above  conditions  are  fulfilled,  then 
examine  car  wiring  for  a  broken  wire  or  a  loose 
connection.  Failing  to  find  the  trouble,  report  to 
the  car  starter  or  person  in  charge. 

5.  If  the  General  Electric  Company's  series-par- 
allel controller,  form  K,  is  used,  the  motorman's 
attention  is  directed  chiefly  to  noting  that  every- 
thing about  the  switches  and  contact  points  and 
cable  connections  in  the  controller  are  in  good 
order.  Two  switches  are  located  in  the  lower  part 
of  these  controllers.  The  one  to  the  right  when 
thrown  up  as  far  as  it  will  go  cuts  out  motor  No. 
1,  or  the  motor  nearest  the  fuse  box  ;  the  switch 
to  the  left  when  thrown  up  cuts  out  motor  No.  2, 
or  the  one  farthest  from  the  fuse  box.  A  small 
quantity  —  enough  only  to  form  a  very  thin  film  — 
of  vaseline  should  be  used  on  the  contact  strip  in 
all  controllers  to  prevent  any  cutting  or  wearing. 

In  both  controllers  of  this  type  the  upper  cut- 
cut  plug  cuts  out  the  same  motor,  which  is  desig- 
nated as  No  1.  The  motorman  should  find  out 
which  is  motor  No.  1,  so  that  he  will  be  able  to 
remove  the  proper  cut-out  in  case  of  trouble  with- 
out experimenting.  It  is  recommended  that  the 
number  of  each  motor  be  painted  on  it  where  the 
motorman  can  see  it.  These  cut-outs  are  designed 
to  be  used  only  in  case  of  trouble.  When  either 
plug  is  removed,  the  starting  of  the  car  is  delayed 
until  after  the  controlling  handle  has  passed  the 
third  notch.  Hence,  in  starting  with  one  cut-out 
plug  removed)  throw  the  handle  directly  to  the  fourth 
notch. 


204  ELECTRIC   RAILWAY   MOTORS. 

6.  The  reversing  switch  determines  the  direction 
in  which  the  current  shall  flow  through  the  motor 
fields   when   it  is   turned   on  by  the   controlling 
handle.     In  the  Westinghouse  apparatus,  for  in- 
stance, the   reversing  switch    has   three   notches. 
The  central  one,  at  which  the  handle  is  placed, 
cuts  off  all  current  from  the  motor  fields,  so  that 
in   this  position  operating  the  controlling  handle 
has  no  effect.     When  it  is  desired  to  start  the  car, 
first  see  that  the  controlling  and  reversing  handles 
are  at  the  "  off"  position  ;  second,  close  canopy  or 
hood  switch  ;  third,   throw   the  reversing  switch 
forward  or  backward,  according  as  it  is  desired  to 
go  in  one  direction  or  the  other;  fourth,  throw  the 
controlling  handle,  and  the  car  will  start. 

Throwing  the  reversing  switch  entirely  over  re- 
verses the  direction  of  the  current  in  the  fields, 
but  this  should  never  be  done  unless  the  control- 
ling handle  is  at  "  off,"  otherwise  the  rush  of  cur- 
rent through  the  coils  which  will  be  due  to  the 
counter  electromotive  force  of  the  motor  added  to 
that  of  the  line  and  that  due  to  the  discharge  of 
the  magnetism  of  the  fields  will  be  so  great  as  to 
endanger  the  coils. 

7.  When  throwing  the  controller  arm  to  "off," 
the  movement  should  be  rapid,  especially  in  pass- 
ing the  first  point,  so  as  to  avoid  drawing  an  arc. 

8.  If   the   controlling   arm   should   go   hard  or 
stick,  do  not  force  it,  as  this  would  only   make 
matters  worse.     Pull  down  the  trolley  or  open  the 
canopy  switch,  or,  better,  do  both,  then  remove 
cover  of  controller.     An  inspection  will  probably 
show  that  the  trouble  is  due  to  want  of  oil,  rough- 
ness of  contacts,  or  something  of  this  kind,  which 
can  easily  be  corrected. 

9.  Never  run  with   trolley  in  wrong   direction 


SPECIFIC    DIRECTIONS    TO    MOTORMEN.          205 

except  in  cases  of  extreme   necessity,   and   then 
very  slowly. 

10.  Never  stop  car  so  that  the  trolley  wheel  will 
be  directly  under  a  circuit  breaker  in  the  line. 

11.  Always  have  current  shut  off  when  trolley 
wheel  is  passing  over  a  circuit  breaker  in  the  line, 
else   the  wheel   in  passing  off  will  draw  an  arc, 
which  tends  to  damage  both  line  and  wheel. 

12.  Never  leave  car  without  removing  the  con- 
troller handles  and  opening  canopy  switches. 

13.  Never  reverse  the  motors  when  the  car  is 
running  except  in  cases  of  extreme  necessity,  such 
as  avoiding  a  collision  or  to  save  a  life.     In  these 
cases  reverse  the  current  in  the  controller,  keeping 
the  handle  on  the  first  or  second  notch   until  the 
car  begins  to  move  backward.     Remember  that 
if  reversal  takes  place  with  controller  at  too  high 
a  notch  the  wheels  will  lose  their  adhesion  to  the 
rails  and  spin  around  backward,  and  the  car  will 
not  stop  so  quickly  as  if  they  kept  revolving  in  a 
forward  direction. 

14.  Go  around  curves  slowly,  using  third  notch. 

15.  When    entering   a   turn-out  or   curve,  the 
conductor   should   be   on  the   rear  platform   and 
should  have  the  trolley  rope  in  hand. 

16.  Slow  up  at  all  street  and  railway  crossings, 
at  all  rough  places  in  the  track,  and  pass  overhead 
switches  with  the  current  thrown  off. 

17.  It  is  better  not  to  stop  on  very  heavy  grades, 
or  on  or  just  before  entering  curves,  if  it  can  be 
avoided,  on  account  of  the  extra  current  required 
for  starting  up  again  under  such  conditions. 

18.  Ordinarily  in  stopping  the  car  always  release 
the  brake  somewhat,  just  before  the  car  comes  to 
a  dead  stop.     Do  not  let  the  brake  fly,  or  kick  the 
brake  dog  off,  for  if  you  do  the  armature  will  take 


206  ELECTRIC    RAILWAY    MOTORS. 

up  the  lost  motion  in  the  gears,  and  when  starting 
again  it  will  necessarily  be  with  a  jerk.  This  is 
unpleasant  to  the  passengers  and  hard  on  both 
motors  and  gears. 

19.  Do  not  keep  brakes  on  in  rounding  curves. 
This  has  been  advocated,  but  is  wrong  and  involves 
a  useless  waste  of  power  at  the  worst  possible  time. 
It  is  one  of  the  commonest  and  worst  mistakes 
motormen  make.     It  is  well  to  have  the  brake  in 
hand  so  that  it  can  be  instantly  applied  if  neces- 
sary, but  it  should  be  entirely  "  off." 

20.  Motormen  should  never  run  the  car  when 
the  trolley  is  off,  especially  down  grade,  for  if  the 
brake  should  fail  he  could  not  reverse. 

21.  In   descending   a  grade   it   is   best  to   run 
slowly,  for  should  it  be  necessary  to  stop  suddenly 
it  would  be  impossible  to  do  so  if  the  speed  were 
high. 

22.  If,  in  wet  weather,  when  climbing  a  grade 
the  wheels  slip,  gradually  work  the  controller  arm 
toward  the  first  point,  throwing  it  to  the  position 
of  "  off"  if  necessary,  until  the  wheels  get  a  grip, 
then  work  the  arm  gradually  over  toward  "  full 
power"  again. 

23.  In  applying  brakes  on  down  grade  be  sure 
not  to  allow  the  wheels  to  get  to  slipping,  for 
when  they  once  commence  to  slip  or  "  skid  "  they 
are  of  veiy  little  use  in  stopping  the  car.     Many 
accidents  have   occurred  in   this  way.     This  pre- 
caution  is  especially   necessary   where   stops   are 
made  on  a  descending  grade.     Should  the  wheels 
begin  slipping,  however,  better   let   the  car  run 
faster  for  a   few   moments   until   they  get  hold 
again,  and  then  apply  the  brakes  gradually  until 
the  car  is  under  control. 

24.  Run  slowly  through  flooded  places,  if  possi- 


SPECIFIC    DIRECTIONS    TO    MOTORMEN.          207 

ble,  with  current  cut  off.  When  examining  motors, 
never  allow  water  to  drip  from  clothing  or  hat 
into  the  motors. 

25.  If  car  won't  start  on  dry  or  dirty  rail,  put 
controller  arm  on  first  or  second  point  and  rock 
the  car.     If  this  fails  to  accomplish  the  purpose, 
have  conductor   take  a  piece  of   wire   or  switch 
stick  and  rub  one  end  of  it  against  the  rear  tread 
of  the  wheel  while  the  other  end  is  pressed  against 
the   rail.     In   case   an   uninsulated   wire   is  used, 
break  contact  at  the  wheel  first,  keeping  the  other 
end  against  the  track,  else  a  shock  will  be  received. 

26.  Never  attempt  to  put  in  a  new  fuse  unless 
canopy  switch  is  open  or  the  trolley  is  off  ;  other- 
wise you  may  get  a  shock  and  damage  the  fuse 
connections  also. 

27.  Should  it  be  found  impossible  at  any  time 
to  start  the  car,  try  the  following  until  the  trouble 
is  located  : 

a.  If   there   is   no  evidence   of  current,  notice 
other  cars.     If  they  are  all  right,  the  trouble  is  in 
your  own  car. 

b.  Throw  on  lamp  circuit.     If  the  lamps  light 
up,  the  trolley  and   ground   wires  are   all  right. 
Now  work  controller,  and  if  the  lights  go  down  or 
out  the  trouble  is  probably  due  to  poor  contact 
between  the  wheels  and  the  rails  (try  25),  or  the 
section  of  track  on  which  the  car  is  standing  may 
be  "  dead."     Use  a  longer  wire  and  connect  wheel 
with  another  rail,  as  in  25. 

If  lamps  do  not  light,  examine  lamp  fuse  box  to 
see  that  fuse  is  not  blown,  and  make  sure  that 
ground  connection  is  not  broken.  Make  sure  that 
lamps  have  good  connection  in  the  socket.  If 
they  still  fail  to  light,  you  may  be  reasonably  sure 
the  power  is  off. 


208  ELECTRIC   RAILWAY    MOTORS. 

c.  Ascertain  whether  the  fuse  has  been  blown. 
If   so,   throw    canopy   switch    and   put    in   new 
fuse  (26). 

d.  See  that  both  motor  cut-outs  are  in  place. 

e.  Try  both   controllers,  and  if  one  works  the 
trouble  is  probably  due  to   poor  contact  in  the 
other.     In  this  case  throw  canopy  switch,  remove 
the  cover  of  the  controller  and  examine  the  con- 
tact blocks   to    see   that   they   all    make   proper 
contact. 

/.  Examine  the  brushes  of  the  motors  to  see 
that  they  are  not  broken,  and  that  they  make  good 
contact. 

28.  In  case  current  is  shut  off  at  station  for  any 
reason  while  the  car  is  running,  bring  controller  to 
"  off  "  position  immediately.     Then  turn  on  light 
circuit,  and  wait  until  the  lamps  light  up  ;  when 
they  have  reached  their  usual  brilliancy,  but  not 
before,  start  the  car.      The  reason  for  this  precau- 
tion  is  that,  should  you  turn  the  controller  far 
enough  to  start  the  car  before  the  full  current  was 
on,  there  would   be  little  or  no  counter  electro- 
motive force  generated  to  keep  back  the  rush  of 
current   when   it   did   come,  and   your   armature 
might  be  injured  either  by  heat  or  by  the  sudden 
jerk  that  would  result. 

29.  In  case  the  brakes  of  a  car  fail  to  operate 
there  are  two  methods  of  stopping  the  car  by  the 
use  of  the  motors.     The  first  consists  in  reversing 
the  direction  of  the  current  in  the  motor  fields  as 
follows  : 

a.  See  that  the  controlling  handle  is  at  "  off." 

b.  Reverse  the  reversing  switch. 

c.  Throw  the  controlling  handle  around  to  the 
first  or  second   notch  —  never  beyond   the    third 
notch,  unless  the  fuse  blows.     In  that  case  (West- 


SPECIFIC    DIRECTIONS    TO    MOTOEMEN.          209 

inghouse)  move  the  handle  around  to  the  last 
notch  and  leave  it  there.  This  converts  the  motor 
into  a  generator  and  it  will  come  -to  a  stop  if  on 
level,  or  if  on  a  grade  will  slacken  up.  In  other 
makes  (Short)  the  simple  pulling  over  of  the 
reversing  lever  after  the  controlling  lever  is 
turned  to  "  off  "  will  accomplish  the  same  thing. 

The  second  method  will  operate  successfully 
whether  the  trolley  is  off  or  on  the  wire.  It  is  as 
follows  : 

a.  Place  controlling  handle  at  "  off." 

b.  Throw  canopy  switch  to  "  off." 

c.  Reverse  the  reversing  switch. 

d.  (Westinghouse.)     Throw   controller   handle 
around  to  last  notch  and  leave  it  there  until  the 
car  stops.     The  step  c  converts  Short  motors  into 
generators.     The  additional  step,  d,  is  required  in 
Westinghouse  motors. 

When  cars  are  running  away  downhill,  the 
method  of  short-circuiting  the  motors  on  them- 
selves and  thereby  converting  them  into  generators 
is  recommended  as  a  last  resort. 

30.  In  case  a  motor  bucks  or  flashes,  examine 
brush  holders,  and  if  they  are  covered  with  dirt 
or  mud,  open  canopy  switch   and  clean  them.     A 
loose  joint  in  the  circuit  between  the  brushes  and 
the  field  will  almost  invariably  produce  flashing  ; 
trace  circuit  carefully  and  find  it.     See  that  the 
spring  is  tight  and  that  there  is  no  dirt  coating  on 
the  bearing  surface  of  the  brush. 

31.  If  the  trouble  is  not  found  with  the  brush 
holder,  and  motor  has  a  peculiar  smell  like  burned 
rubber  or  shellac,  wait  for  the  next  car  to  push 
her  in. 

32.  Motormen    should    always  have   a   wrench 
on  car  to  tighten  up  a  loose  nut,  and  should  be 


210  ELECTRIC   RAILWAY   MOTORS. 

constantly   on   the   lookout   for   troubles  of  this 
kind. 

33.  Always  report  to  inspector  any  trouble  with 
track,  such  as  "  dead  "  rail,  or  of  trolley  wire,  such 
as  break  of  line  or  insulator,  etc.,  and  any  unusual 
noises  of  motors,  having  first,  however,  endeavored 
to  account  for  these  latter  yourself. 

34.  When  you  desire  to  run  at  slower  speed  and 
controller  is  full  on,  it  is  usually  considered  better 
to  first  pull  it  clear  back  to  starting  point  and  then 
back  to  position  you  think  will  give  the  desired 
speed. 

35.  Never  pull  reversing  lever  over  while  con- 
troller is  on.    If  you  do,  you  are  likely  to  blow  the 
fuse  or  burn  up  the  motor,  in  either  case  losing 
control  of  your  car. 

36.  If  in  running  along  you  feel  the  car  sud- 
denly let  up,  throw  controller  off  and  ascertain  the 
cause  if  you  can.     It  may  be   the  trolley  is  off, 
passing  a  trolley  break,  a  fuse  blown  or  current 
cut  off  at   the  power  house. 

37.  If  you  do  not  find  any  trouble,  try  to  start 
again.     If    the   car   does   not   move,   proceed   as 
directed   under  such  circumstances. 

38.  Do  not  run   over  sticks,  wire  or  other  ob- 
structions on  the  track,  as  they  are  liable  to  get 
entangled  in  the  motor.     Get  down  and  remove 
them. 

39.  If  paving  blocks  or  other  projections  stick 
out  above  the  pavement,  slow  up  and  be  sure  the 
motor   will   pass   over   without    touching    before 
attempting  to  pass.     Of  course  you  will  remove 
the  obstruction,  if  possible. 

40.  In  case  of  the  repeated  blowing  of  the  fuse 
without  apparent  cause,  pull  down  your  trolley 
and  wait  to  be  pushed  in. 


SPECIFIC    DIRECTIONS    TO    MOTORMEN.          211 

41.  The  proper  handling  of  a  car  on  a  curve  is 
perhaps    the   most   difficult    task    that  the   new 
motorman  has  to  learn.     A  good  rule  is  the  follow- 
ing:  In  approaching  a  curve  cut  off   your  con- 
troller, and  bring  the  car  down  to  a  slow  walk  be- 
fore entering,  and  have  your  brake  in  hand,  but 
free,  unless  it  be  down  grade.     This  will  let  the 
car  run  into  the  curve  easily  and  without  shock. 
As  soon  as  you  feel  that  the  car  is  fairly  on  the 
curve    apply  sufficient  current  to  carry  the   car 
around  the  curve  at  about  the  same  rate  of  speed, 
cutting  it  off  again  just  before  leaving  the  curve. 
This  will  allow  the  car  to  take  the  tangent  with 
the  least  possible  shock. 

Always  bear  in  mind  that  anything  that  causes 
the  car  to  jerk  is  wrong. 

42.  If  your  car  leaves  the  track,  do  not  attempt 
to  run  her  back  with  the  current  until  you  are 
sure  she  can  roll  freely  without  jamming.     Move- 
ment of  the  switch  when  the  wheels  cannot  turn, 
or  are  not  turning  freely,  is  likely  to  cause  trouble 
both  with  the  motor  and  with  the  switch. 

43.  Avoid  carelessness.    Do  not  allow  any  metal, 
viz.,  your  oil  can,  etc.,  to  touch  brass  screws  on 
motor  boards  unless  the  trolley  is  off  the  wire. 
Do  not  handle  the  screws  unless  the  trolley  is  off 
or  your  person  touches  nothing  but  dry  wood. 

44.  When  examining  the  motor  while  the  car  is 
in  motion,  face  the  rear  of  the  car,  or  so  place 
yourself  that  any  jerk  as  in  sudden  stopping  will 
not  pitch  you  into  the  machinery. 

45.  Whenever  the  trolley  leaves  the  wire  the 
conductor  should    signal  the  motorman   to   stop, 
and  then,  after  replacing  the  trolley,  he  should 
signal  to  go  ahead.     The  motorman  should  bring 
controller  to  "  off"  position  as  soon  as  the  trolley 


212  ELECTRIC    RAILWAY    MOTORS. 

jumps  and  keep  it  there  until  the  conductor  sig- 
nals to  proceed. 

46.  If  you  notice  any  loose  motion  about  the 
trolley,  or  if  it  leaves  the  line  frequently,  or  if, 
when  running  fast  on  a  straight  track,  there  is  any 
flashing  between  the  trolley  and  the  wire,  report 
the  same  at  once. 

47.  Remember  that  the  trolley  wheels  need  oil- 
ing.    This  should  be  done  as  often  as  necessary. 
The  oil,  especially  in  cold  weather,  should  be  of  a 
quality  that  will  not  become  gummy  or  sticky. 

48.  Watch  your  track  joints  when  going  toward 
a  station.     If  there  is  sparking  ahead  of  you  at 
the  joints,  the  rail,  connections  are  broken.     If  the 
car  suddenly  gathers  speed  after  passing  any  point, 
or  if  when  the  lights  are  on  they  become  very  dim 
and  then  suddenly  brighten  up,  a  broken  or  loose 
track  connection   is  also  indicated.     Report  the 
fact  and  place  promptly. 

49.  Observe  carefully  whether  the  car  takes  her 
natural  speed  for  all  positions  of  the  switch,  and 
if  not  report  trouble,  or,  better  still,  find  it  your- 
self and  correct,  if  possible. 

50.  If  motor  or  car  seems  to  work  hard,  feel  of 
bearings ;  if  one  or  more  are  hot,  apply  oil  and 
watch  frequently;  if  heat  increases,  the  car  should 
be  run  in  and  inspected. 

51.  If  journals  squeak,  it  means  that  they  are 
running  dry  and  require  oil. 

52.  When  storing  your  car  in  the  house  for  the 
night,  remove  the  trolley  from  the  wire,  cut  out 
the  safety  switch,  turn  the  reverse  lever  so  that 
the  car  will  be  ready  to  run  out.     Take  off  the 
levers  and  place  them  on  the  hook  in  the  office 
provided  for  them  and  marked  by  the  number  of 
the  car. 


CHAPTER  XXIII. 

INSTBUCTIONS   TO    INSPECTORS     AND    SUPERINTEND- 
ENTS. 

UPON  you  depends,  more  than  upon  anyone  else, 
the  success  or  failure  of  any  electrical  system  that 
is  placed  in  your  hands,  provided,  of  course,  the 
system  in  question  is  a  fairly  good  one.  Cases  are 
not  unknown  where  a  given  electric  system  has 
proved  a  failure  under  one  superintendent  and 
made  to  work  satisfactorily  in  every  way  by  his 
successor.  The  reverse  is  also  often  the  case  :*that 
a  success  has  been  changed  to  failure  by  the  trans- 
fer of  the  management  from  the  hands  of  a  com- 
petent man  to  those  of  one  unqualified  for  this 
most  important  position.  The  first  requisite  in  an 
inspector  or  superintendent  is  that  he  shall  be 
familiar  with  every  detail  of  the  system  with 
which  his  cars  are  equipped.  If  it  is  important 
that  the  motormati  shall  be  familiar  with  his  appa- 
ratus, it  is  much  more  important  that  his  superiors, 
from  whom  he  receives  instruction,  should  know  it 
also  and  in  a  broader  sense.  You  must  remember 
that  the  motorman  is  largely  what  you  make  him. 
He  comes  to  you,  perhaps,  an  untrained  hand  ; 
perhaps,  what  is  still  worse,  he  has  had  instruction 
on  another  line  by  a  superintendent  who  was  incom- 
petent or  careless,  and  has  thereby  acquired  habits 
which  he  must  first  unlearn. 

You  must  realize  that  as  you  are  responsible  to 

213 


214  ELECTRIC    RAILWAY    MOTORS. 

your  company  for  the  proper  working  of  the  road, 
so  you  must  hold  those  under  you  responsible  to 
yourself.  Your  reputation  and  success  are  there- 
fore largely  dependent  upon  the  fidelity  and  ability 
of  those  whose  training  is  in  your  care.  Appre- 
ciating this,  you  will  first  train  yourself.  Procure 
from  the  company  wrhose  apparatus  you  are  using 
full  instructions  as  to  the  handling  of  their  ma- 
chinery, together  with  blue  prints  showing  the 
wiring  and  connections  of  each  individual  circuit 
connected  with  the  electrical  equipment  of  your 
system.  If  not  an  electrician  yourself,  you  should 
call  in  someone  who  is,  and  who  can  and  will  go  over 
with  you  every  detail  of  your  system,  and  explain 
the  whys  and  wherefores  of  everything  connected 
with  your  plant.  Try  to  understand  everything 
intelligently,  and  then  try  your  hand  at  imparting 
this  knowledge  to  the  mptormen,  in  wrhose  hands 
your  reputation  and  success  so  largely  lie.  It  is 
the  experience  of  those  who  have  tried  it  that  the 
best  way  to  learri  a  thing  accurately  one's  self  is  by 
trying  to  teach  others  what  you  partly  know  your- 
self. This  is  true  in  mathematics,  it  is  true  in 
science  in  general  and  it  is  true  in  the  car  stables, 
and  ,the  superintendent  who  tries  most  to  impart 
knowledge  to  those  under  him  will  in  a  short  while 
outstrip  in  knowledge  him  who  perhaps  at  first 
knew  more,  but  who  through  a  mistaken  idea  of 
the  dignity  or  importance  of  his  position  has  kept 
his  knowledge  to  himself. 

The  various  means  by  which  he  himself  has 
gained  his  knowledge  should  as  far  as  possible  be 
placed  at  the  disposal  of  his  employees,  and  they 
should  be  encouraged  in  every  way  to  avail  them- 
selves of  them  to  the  fullest  extent.  In  fact,  a 
motorman  who  will  not  avail  himself  of  such 


TO    INSPECTORS   AND   SUPERINTENDENTS.       215 

opportunities  when  offered  is  an  unsafe  man  to 
trust  with  a  car.  On  some  roads  the  plan  has  been 
successfully  adopted  of  furnishing  each  motorman 
a  diagram  of  the  connections  that  are  being  made 
as  the  handle  of  the  controlling  lever  is  moved  from 
point  to  point.  On  this  diagram  are  also  given  a 
few  of  the  most  important  instructions,  and  these 
instructions  are  supplemented  by  verbal  ones  from 
time  to  time  as  occasion  requires.  Some  roads 
also  provide  a  reading  room  for  their  employees, 
where  a  few  standard  works  of  reference  on  elec- 
trical subjects,  and  the  street  railway  and  electrical 
papers,  are  kept  on  file.  This  is  an  excellent  plan, 
and  another  one  is  to  hang  upon  the  wall  of  the 
car  house  or  other  convenient  place  large  diagrams 
of  the  motor  connections  and  wiring  circuits  of 
the  car.  If  equipments  of  more  than  one  system 
of  control  or  make  are  used  on  the  line,  each  should 
be  similarly  represented,  so  that  the  differences 
will  be  apparent  to  those  who  are  to  manage  them. 
These  diagrams  might  with  profit  be  drawn  to  half 
size,  or  even  larger,  and  in  order  that  the  different 
circuits  may  be  the  more  readily  distinguishable, 
they  should  be  designated  by  different  colors  and 
the  various  parts  of  the  equipment  lettered  for 
ready  reference.  These  should  be  hung  where  the 
motormen  are  most  apt  to  congregate  when  not  on 
duty  on  their  cars,  so  that  they  may  discuss  them 
at  their  leisure. 

A  spirit  of  emulation  among  the  motormen  as 
to  the  best  care  of  the  equipment  of  their  cars  and 
fulfillment  of  schedule  time  should  be  fostered, 
and  to  this  end  a  motorman  should  be  kept  on  the 
same  car  as  much  as  possible.  That  car  should, 
as  far  as  possible,  be  considered  his  own,  and  he 
should  be  held  responsible  for  its  record.  Nothing 


216  ELECTRIC    RAILWAY    MOTORS. 

is  so  subversive  of  effective  service  as  the  frequent 
change  of  assignment  of  cars.  No  motorman  can 
be  held  responsible  for  the  monthly  record  of  a 
car  which  has  been  handled  by  a  dozen  others 
beside  himself,  nor  can  he  take  a  personal  pride  in 
its  condition  at  the  end  of  the  month  under  such 
conditions. 

Mr.  P.  P.  Sullivan  of  the  Lowell  and  Suburban 
Street  Railway  Company,  in  speaking  on  this  sub- 
ject at  a  monthly  meeting  of  the  Massachusetts 
Street  Railway  Association,  said  :  "  In  addition  to 
creating  an  interest  among  the  men,  and  in  fact 
to  help  create  such  interest,  we  have  prizes  for  the 
motormen  whose  cars  have  had  the  best  records  in 
point  of  expense,  delays,  etc.,  and  in  this  manner 
we  are  also  enabled  to  find  out  from  the  regular 
men  who  the  best  relief  men  are.  Motormen  are 
given  printed  forms  which  enable  them  to  call  the 
attention  of  the  night  foreman  to  certain  things 
which  may  appear  wrong,  and  such  form  is  coun- 
tersigned by  such  foreman  and  forwarded  to  the 
superintendent.  All  loss  of  mileage  or  taking  off 
of  cars  is  reported  directly  to  the  manager's  desk, 
who  exacts  an  accounting  for  the  cause  from  the 
superintendent.  By  following  the  above  methods 
we  have  been  enabled  to  adopt  a  standard  of  car 
mile  expenses,  and  the  different  foremen  are  given 
to  understand  that  if  the  expenses  are  kept  below 
such  a  figure  they  may  expect  a  present  at  the  end 
of  the  fiscal  year." 

He  further  says  :  "  We  assume  that  a  man  be- 
fore taking  charge  of  a  car  is  absolutely  ignorant, 
has  no  interest  in  the  apparatus,  and  we  aim  to 
teach  him,  we  endeavor  to  excite  his  interest  and 
curiosity,  so  that  he  will  look  out  for  his  motors, 
inquire  for  certain  motors,  create  a  rivalry  so  that 


TO    INSPECTORS    AND    SUPERINTENDENTS.       217 

a  man  will  boast  of  his  record  ;  and  we  have  such 
instances. 

"In  the  car  house  skilled  mechanics  are  in 
charge  who  are  held  responsible  for  results ;  sub- 
division of  duties  and  labors  in  relation  to  parts  of 
machinery  as  far  as  practicable  is  practiced,  so  as 
to  more  readily  locate  responsibility.  The  object 
is  that  when  a  car  leaves  the  shop  newly  equipped 
such  equipment  shall  be  thoroughly  done,  through 
the  best  material  and  workmanship,  and  after  that 
time  a  thorough  inspection.  Motors,  trucks,  and 
cars  are  numbered,  and  an  official  record  is  then 
begun,  and  date  and  description  of  any  repairs 
made  are  kept  and  comparisons  formed  and  causes 
sought." 

The  ideas  above  suggested  will  readily  com- 
mend themselves  to-  everyone  who  is  not  penny 
wise  and  pound  foolish,  for  experience  has  already 
amply  demonstrated  that  good  system,  good 
material,  good  workmanship  and  skillful  em- 
ployees who  feel  a  genuine  interest  in  their  work 
are  none  too  good  for  the  best  results. 

But  with  all  this  there  will  be  a  failure  if  the 
cars  are  turned  over  to  the  motorman  in  anything 
but  the  best  condition.  It  must  be  understood 
that  the  motormau  is  usually  not  a  mechanic  and 
he  is  not  an  electrician,  and  that  if  he  were  either 
or  both  he  would  have  but  scant  facilities  for  the 
exercise  of  his  talents  while  operating  his  car  on 
the  road.  He  will  have  done  his  whole  duty  if 
he  handles  intelligently  what  you  give  him  and 
reports  all  troubles  as  soon  as  they  arise. 

In  the  training  of  motormen  it  is  the  practice 
on  some  roads  to  put  them  first  in  the  machine 
and  repair  shops,  so  that  by  this  preliminary 
experience  they  may  get  an  insight  into  the 


218  ELECTRIC    RAILWAY    MOTORS. 

anatomy  of  the  car  equipment  and  the  adjustment 
of  parts  to  each  other.  This  is  certainly  an 
excellent  plan  where  practicable,  and  another  one 
which  is  always  feasible,  but  by  far  too  seldom 
practiced,  is  to  hold  what  the  doctors  would  call 
"  clinics  "  over  disabled  or  diseased  motors  when- 
ever such  are  brought  in.  For  instance,  if  a 
motor  is  sent  to  the  repair  shop  for  sparking  on 
account  of  any  of  the  causes  before  mentioned,  as 
many  of  the  employees  as  it  is  possible  to  gather 
together  should  be  called  to  witness  the  commu- 
tator spark  while  in  action  and  be  told  the  specific 
cause  thereof,  and  then  they  should  be  shown  in 
the  repair  shop  that  the  diagnosis  is  correct  and 
how  the  trouble  is  remedied.  If  a  motorman  has 
once  seen  the  sparking  due  to  an  open  coil,  he  will 
forever  after  recognize  it.  And  so  with  the  other 
troubles — an  object  lesson  such  as  the  one  sug- 
gested will  be  worth  more  than  all  the  verbal 
instruction  you.  can  give. 

Regular  inspection  should  be  made  every  day  if 
possible.  It  does  not  pay  to  allow  cars  to  run 
until  they  absolutely  refuse  to  run  any  longer. 
In  no  case  does  the  old  adage,  "A  stitch  in  time 
saves  nine,"  apply  with  more  force  than  in  this. 
I  cannot,  therefore,  insist  too  strongly  that  repairs 
be  made  just  as  soon  as  it  is  discovered  that  they 
are  required.  If  the  motorman  discovers  trouble, 
he  should  fix  it  if  he  can  •  if  he  can't  fix  it,  he 
should  run  the  car  into  the  stables  at  the  first 
opportunity  and  report.  In  no  case  should  he 
start  out  with  a  car  that  is  not  in  condition,  and  it 
is  the  especial  business  of  the  inspector  to  see  that 
he  does  not. 

One  of  the  leading  manufacturers  of  street  car 
motors,  in  his  instructions  to  inspectors,  says : 


TO   INSPECTORS   AND    SUPERINTENDENTS.       219 

"Let  us  impress  upon  you  the  importance  of  keep- 
ing a  careful  watch  of  all  nuts,  bolts,  screws  and 
all  wire  connections  to  see  that  everything  is 
screwed  up  tight." 

Daily  examinations  of  connections  of  motors, 
trolleys,  lightning  arresters,  fuse  blocks,  etc.,  should 
be  made,  and  especial  attention  should  be  directed 
to  the  connection  between  the  wire  from  the  in- 
terior of  the  car  and  the  trolley  base  to  see  that  it 
is  in  good  condition. 

In  addition  to  the  daily  inspection  at  least  once 
a  month  the  car  should  be  run  over  the  pit  and  the 
equipment  given  a  most  thorough  overhauling. 

For  testing  out  faults  the  magneto  bell  is  an 
instrument  of  great  general  utility,  and  the  mana- 
gers of  electric  roads  will  save  their  inspectors 
much  time  and  trouble  by  providing  one  or  more 
for  their  use. 


CHAPTER   XXIV. 

LOCATING    FAULTS. 

WHEN  starting  a  new  car,  or  one  whose  connec- 
tions have  been  changed,  or  in  fact  any  car  that 
has  come  from  the  repair  shops,  always  try  the 
motors  one  at  a  time  to  see  that  the  revolution  of 
the  controller  handle  moves  the  car  in  the  same 
direction  with  each  motor. 

To  find  an  open  circuit  in  the  car  wiring  try 
both  controller  handles  ;  if  one  works,  the  trouble 
is  probably  in  the  other.  If  neither  works,  the 
trouble  is  probably  not  in  the  controllers.  If  in 
one  controller,  throw  the  canopy  switch  to  "off." 
Now  hold  one  of  the  wires  from  a  magneto  bell  on 
the  iron  work  of  the  truck  or  motors,  and  touch 
successively  with  the  other  wire,  while  the  handle 
of  the  magneto  bell  is  being  rapidly  turned,  the 
different  contact  fingers  on  the  controller  ;  if  they 
ring,  the  ground  connection  through  that  finger  is 
all  right.  If  the  bell  fails  to  ring  through  any  one  of 
the  fingers,  you  have  located  the  circuit  on  which 
the  trouble  exists.  Trace  out  that  circuit  and  cor- 
rect the  trouble.  If  all  points  ring  on  one  con- 
troller, pursue  the  same  method  with  the  other. 
If  both  are  all  right,  look  for  a  break  or  loose  con- 
nection in  the  wire  running  from  the  trolley  base 
to  the  fuse  block,  or  to  the  canopy  switch* 

SWO 


COMMUTATORS.  221 

The  wearing  parts  and  those  requiring  the  most 
careful  attention  are  the  following  : 

COMMUTATORS. 

The  color  of  the  commutator  is  in  itself  a  pretty 
good  guide  as  to  its  condition.  As  long  as  it 
retains  a  good  gloss  and  is  of  a  chocolate  color  it 
probably  does  not  require  attention.  It  should, 
however,  be  carefully  examined  to  see  that  it  is 
clean  and  true. 

To  clean  it  remove  the  brushes,  and  then,  while 
the  car  is  running  with  that  motor  cut  out,  use 
fine  sandpaper  applied  on  a  block  of  wood  which 
exactly  fits  the  curvature  of  the  commutator. 
Never  use  emery  paper,  as  the  emery  itself  is  a 
conductor  of  electricity,  and  particles  detached 
from  the  paper  may  find  lodgment  between  the 
commutator  segments  and  cause  future  short 
circuits. 

In  case  of  high  bars  on  the  commutator  some- 
times they  may  be  hammered  down  by  placing  a 
piece  of  wood  or  leather  between  the  hammer  and 
the  block.  Never  hammer  a  commutator  block 
directly  with  the  hammer,  however,  as  it  is  likely 
to  flatten  out  the  surface  so  that  it  will  extend 
over  the  insulating  mica  between  it  and  the  next 
block,  causing  a  short  circuit.  Some  authorities 
say  that  a  hammer  should  never  be  used  at  all, 
and  that  the  high  block  should  be  filed  down. 
But  whatever  the  remedy,  a  commutator  that 
presents  either  high  bars  or  flats  must  be  abso- 
lutely true  after  treatment,  and  this  can  only  be 
insured  by  turning  it  down  on  the  lathe. 

The  lathe  is  the  remedy  also  for  a  rough  or 
eccentric  commutator  or  for  mica  projecting  be- 


222  ELECTRIC    RAILWAY    MOTORS. 

yond  the  surface,  as  well  as  for  unevenly  worn 
commutators.  The  turning  down  of  a  commuta- 
tor, however,  is  a  nice  piece  of  work,  and  should 
only  be  intrusted  to  experienced  hands.  The 
cutting  should  not  go  deeper  than  is  absolutely 
necessary  to  remove  the  difficulty,  and  should  not 
extend  to  the  outer  end  of  the  commutator  ;  a 
narrow  ridge  should  always  be  left  on  the  edge. 
Crocker  and  Wheeler  say:  "In  turning  a  commu- 
tator in  a  lathe  a  diamond-pointed  tool  should  be 
used,  this  being  better  than  either  a  round  or 
square  end.  The  tool  should  have  a  very  .sharp 
and  smooth  edge,  and  only  an  exceedingly  fine  cut 
should  be  taken  off  each  time  in  order  to  avoid 
catching  in  or  tearing  the  copper,  which  is  very 
tough.  The  surface  is  then  finished  by  applying 
a  'dead  smooth'  file  while  the  commutator  re- 
volves rapidly  in  the  lathe."  After  turning  down 
or  sandpapering  the  spaces  between  the  commu- 
tator blocks  should  be  carefully  examined  for 
copper  dust  or  other  conducting  material.  If 
found,  such  should  be  removed.  The  commutator 
should  be  carefully  lubricated  from  time  to  time, 
great  care  being  taken,  however,  not  to  use  an 
excess.  A  little  vaseline  is  perhaps  as  good  a 
lubricator  as  anything  for  either  the  commutator 
or  controlling  switch. 

The  brushes  should  be  examined  frequently, — 
once  a  day  is  not  too  often, — and  the  brush  holders 
should  be  cleaned  whenever  found  to  be  dirty. 
Brush  holders  should  never  be  permitted  to  be- 
come loose,  and  the  brushes  should  not  be  allowed 
to  become  too  short,  for  in  this  case  in  the  adjust- 
ment of  the  holders  the  springs  will  not  give  suffi- 
cient pressure  for  good  contact.  Brushes  should 
fit  curve  of  commutator  perfectly,  and  new  ones 


DROP  METHOD  OF  TESTING  FOE  FAULTS.        223 

should  be  filed  or  sandpapered,  if  necessary,  to 
make  a  good  fit.  Brush  tips  should  be  kept  clean, 
and  should  not  be  allowed  to  become  wedged  in 
the  holders. 

THE  DROP  METHOD  OF  TESTING  FOR  FAULTS. 

While  it  is  entirely  beyond  my  province  to  dis- 
cuss the  methods  of  electrical  testing  at  this  time, 
there  are  one  or  two  simple  methods  that  are  so 
generally  available  that  it  seems  well  to  introduce 
them  here. 

If  a  break  or  bad  contact  in  a  circuit  is  suspected, 
it  may  be  readily  located  by  what  is  known  as  the 
"  drop  method."  This  is  founded  on  the  principle 
that  if  everything  is  normal  in  a  circuit  the  resist- 
ances between  any  two  points  equidistant  on  that 
circuit  should  be  about  the  same.  If  one  terminal 
of  A  galvanometer  be  fastened  to  one  point  of 
a  circuit,  and  the  other  be  successively  applied  to 
other  points  on  the  same  circuit  at  equally  increas- 
ing distances,  the  needle  will  register  in  a  circuit 
which  is  intact  a  regular  increase  of  deflection 
with  every  successive  point  touched.  The  reason 
for  this  is  that  the  galvanometer,  being  con- 
nected up  in  parallel  with  the  conductor,  registers 
the  relative  resistance  of  the  portion  of  the  circuit 
tested  and  that  of  its  own  circuit.  The  latter  being 
fixed,  the  indications  will  be  greater  as  the  resist- 
ance of  the  circuit  measured^is  greater.  If  when 
the  galvanometer  wire  touches  a  new  point  on  the 
circuit  the  increase  of  deflection  is  much  greater 
than  it  should  be,  it  indicates  that  there  is  trouble 
between  this  point  and  the  last  one  touched.  A 
common  way  of  applying  this  method  is  to  fix  the 
two  terminals  in  a  handle  of  some  kind,  so  that 


224  ELECTRIC    RAILWAY    MOTORS. 

their  distance  is  not  varied,  and  then  move  these 
two  terminals  along  the  circuit.  Since  the  length 
of  wire  measured  in  this  case  is  always  the  same, 
the  reading  of  the  galvanometer  will  always  re- 
main the  same  if  everything  is  right.  If  the  deflec- 
tion increases  at  any  point,  the  trouble  is  at  once 
located  between  the  two  terminals  of  the  galvanom- 
eter. In  testing  for  breaks  in  the  armature  coils 
the  two  points  are  applied  to  adjacent  commutator 
blocks  all  around  the  commutator.  The  deflection 
of  the  galvanometer  should  not  vary  between  any 
two  successive  segments,  but  if  it  does  there  is  a 
loose  connection  or  a  break  somewhere  in  the  coil 
or  connections  between  the  two. 

INSULATIOX   TEST. 

Another  simple  test  that  is  not  only  of  great  use, 
but  also  available  to  even  the  least  technical  if  he 
have  but  a  magneto  bell,  is  the  test  for  insulation 
resistance.  It  is  very  desirable  to  know  that  those 
portions  of  your  apparatus  that  should  be  insu- 
lated from  each  other  are  so  insulated,  as,  for  in- 
stance, the  armature  windings  from  the  armature 
core,  or  the  brush  holder  from  the  brushes.  The 
ordinary  magneto  bell  is  rated  to  ring  through 
from  10,000  to  30,000  ohms  resistance.  If,  there- 
fore, one  terminal  of  the  bell  be  connected  to  each 
of  the  parts  that  should  be  insulated  from  each 
other,  as,  for  instance,  the  armature  shaft  and 
a  commutator  segment,  or  the  brush  and  the  brush 
holder,  and  the  bell  can  then  be  caused  to  ring, 
it  indicates  either  a  very  poor  insulation  between 
the  parts  or  else  a  bad  short  circuit.  Its  failure 
to  ring  does  not,  however,  indicate  that  the  insula- 
tion is  perfect  or  sufficient,  since  it  merely  indi- 


INSULATION  -TEST.  225 

cates  that  the  resistance  is  somewhat  greater  than 
30,000  ohms  (if  that  be  the  resistance  through 
which  it  is  rated  to  ring),  whereas  the  insulation 
resistance  between  armature  coil  and  core  should 
not  be  less  than  100,000  ohms  for  every  100  volts 
used  on  the  circuit.  This  test  should  therefore 
be  considered  only  as  a  crude  one  and  more  as 
a  test  for  short  circuit  than  as  a  test  for  insu- 
lation. 

A  much  more  reliable  test  is  that  known  as  the 
voltmeter  test.  This  requires  a  sensitive  high 
resistance  voltmeter,  such  as  the  Weston.  The 
Weston  150-volt  instrument  usually  has  a  resist- 
ance of  its  own  of  about  15,000  ohms.  (Its  exact 
resistance  is  always  stated  on  a  certificate  pasted 
inside  the  case.)  Apply  the  galvanometer  first  to 
some  circuit  or  battery  having  a  high  electro- 
motive force  —  say  100  volts  —  and  note  the  deflec- 
tion of  the  needle.  Then  connect  the  parts  whose 
insulation  resistance  is  to  be  tested  with  this 
same  circuit  in  series  with  the  voltmeter.  If  the 
armature  resistance  is  to  be  tested,  for  instance, 
connect  one  terminal  of  the  circuit  with  the 
armature  shaft,  and  the  other  with  one  terminal  or 
binding  post  of  the  machine,  and  note  the  new 
deflection.  It  will  be  less  than  before,  because 
an  increased  resistance  (the  insulation  resistance) 
has  now  been  placed  in  series  with  the  galvanom- 
eter resistance.  'The  insulation  resistance  will 
then  be  found  by  the  equation  : 


Insulation  resistance  =  --  JR, 

d 

in  which  D  is  the  deflection  due  to  the  galvanom- 
eter alone  :  d  =  the  deflection  when  the  machine 
is  in  series  with  the  galvanometer,  and  M  is  the 


226  ELECTRIC    RAILWAY    MOTORS. 

resistance  of  the  galvanometer  or  voltmeter.  Thus 
if  the  circuit  employed  in  testing  is  100  volts, 
then  D=1QO.  If  the  second  deflection,  viz.,  that 
through  the  galvanometer  (say  15,000  ohms),  plus 
the  insulation  of  the  machine  is  1,  our  equation 
becomes  :  Insulation  resistance 
100X15,000 

= 15,000  =  1,485,000  ohms. 

1 

BEARINGS. 

The  importance  of  keeping  the  bearings  in  first- 
class  order  will,  of  course,  be  apparent  at  once. 
Be  watchful  at  all  times  that  they  do  not  become 
too  much  worn,  else  the  armature  is  likely  to  strike 
against  the  fields  and  become  ruined.  If,  on  in- 
spection, you  find  that  the  clearance  between  ar- 
mature and  pole  pieces  is  becoming  small,  put  in 
new  bushings  at  once.  Do  not  wait  until  the  clear- 
ance becomes  dangerously  small.  Looseness  of  the 
armature  bearings  can  be  detected  by  lifting  on  the 
armature  first  at  one  end  and  then  at  the  other. 
Loose  bearings  on  the  main  axle  may  cause  gears 
to  break  by  reason  of  their  being  thrown  out  of 
alignment.  The  grease  boxes  on  the  motor  should 
be  given  careful  attention,  and  should  be  filled 
every  night  or  morning  before  the  car  is  sent  out. 
There  is  no  economy  in  using  an  inferior  lubricant — 
rather  the  reverse  ;  but  the  best 'grease  is  liable  to 
thicken,  and  before  adding  fresh  the  old  should  be 
stirred  up  with  a  little  oil.  In  removing  covers  to 
inspect  grease  boxes  be  careful  that  none  of  the 
dirt  or  sand  falls  into  the  boxes.  Occasionally  all 
the  grease  should  be  removed,  the  boxes  thor- 
oughly washed  with  gasoline,  and  a  small  quantity 
allowed  to  run  through  the  bearings  to  cut  any 


OF  THE 


GEARS   AND 

grease  which    may   have   found    lodgment  there 
and  hardened. 

GEARS    AND    PINIONS. 

The  life  of  the  gears  and  pinions  depends  very 
largely  upon  the  intelligent  care  they  receive. 
Proper  lubrication  is  one  of  the  most  largely  con- 
tributive  agencies  toward  long  life,  but  they  should 
be  carefully  examined  every  night  to  see  that  they 
have  not  become  loose  on  the  shaft.  Since  they 
usually  have  tapering  seats,  they  may  be  tightened 
by  firmly  tapping  them  with  a  hammer.  With 
this  frequent  examination  there  is  no  danger  that 
they  will  become  unduly  worn  without  your  knowl- 
edge. Tighten  up  all  the  bolts  whenever  exam- 
ining them.  Drive  up  the  key  or  feather  to  insure 
tightness  of  gears  and  pinions,  and  if  these  are 
too  much  worn  throw  them  away  and  substitute 
new  ones.  The  unusual  "  knocking  "  noises  some- 
times heard  when  the  car  is  in  operation  are 
usually  due  either  to  worn  keys,  worn-out  gears  or 
to  some  hard  object  which  has  become  lodged 
between  the  teeth.  This  knocking  sound  is  a 
warning  that  must  be  heeded  at  once,  and  the 
above  causes  are  the  first  to  be  suspected.  Investi- 
gate, and  if  the  pinion  is  worn  out  throw  it  away 
and  put  on  a  new  one  with  a  new  key.  A  new 
pinion  will  not,  however,  go  well  with  an  old  and 
worn  gear.  If  the  gear  be  but  slightly  worn  and 
too  good  to  throw  away,  keep  it  to  go  with  some 
slightly  worn  but  equally  good  pinion,  but  don't 
allow  a  new  wheel  to  mesh  into  an  old  one. 

On  fitting  new  gears  note  carefully  that  the 
teeth  mesh  properly  before  putting  them  into  use. 
This  is  best  done  by  revolving  the  armature  by 
hand  while  the  car  is  jacked  up.  The  fitting  of 


228  ELECTRIC   RAILWAY   MOTORS. 

new  gears  is  a  nice  operation,  and  should  not  be 
intrusted  to  any  but  a  responsible  person. 

CONTROLLERS. 

The  controllers  should  be  thoroughly  overhauled 
every  night  ;  the  contact  rings  and  fingers  cleaned 
and  polished  when  found  to  be  rough,  and  a  little 
vaseline  rubbed  on  ;  the  screws  that  hold  the  con- 
tact rings  should  be  tightened  if  loose,  and  the 
ratchet  wheel  and  pawl  at  the  top  of  the  cylinder, 
as  well  as  the  upper  and  lower  bearings  of  the 
cylinder,  should  be  carefully  lubricated,  taking 
care,  however,  that  too  much  lubricant  is  not  used 
and  that  it  does  not  run  down  upon  the  cylinder. 
In  equipments  not  emp^dng  the  usual  platform 
cylinder  the  equivalent  parts  beneath  the  car 
should  receive  their  appropriate  attention.  When- 
ever a  part  becomes  worn  it  should  be  replaced. 
In  fact,  the  directions  in  regard  to  the  controlling 
devices  may  all  be  summed  up  thus  :  See  that  they 
are  in  perfect  order  every  night  or  morning  before 
the  car  leaves  the  stables. 


CHAPTER  XXV. 

TROLLEY     WHEELS. 

THE  life  of  the  trolley  wheel  depends  upon  the 
quality  of  the  metal,  the  number  of  miles  that  it 
travels  and  the  care  that  it  receives.  Remember 
that  its  speed  is  enormous.  Take  a  trolley  wheel 
that  is  6  inches  in  diameter,  for  instance.  When 
the  car  is  running  at  8  miles  an  hour,  a  36-inch  car 
wheel  will  make  4482  revolutions,  and  we  know 
the  necessity  of  lubrication  for  this.  At  the  same 
speed  and  in  the  same  time  a  4-inch  trolley  wheel 
will  make  126,720  revolutions,  and  yet  we  are  liable 
to  overlook  the  necessity  for  lubrication  here.  In 
fact,  the  trolley  wheel  is  subject  to  something  far 
worse  than  frictional  wear,  viz.,  sparking.  Every 
time  a  spark  occurs  on  a  trolley  it  means  the  com- 
bustion of  so  much  copper.  Oil  the  trolley  wheel  in 
the  J)arn,  therefore,  as  often  during  the  day  as  it 
is  practicable.  Instruct  your  motorman  to  oil  it 
when  he  has  an  opportunity.  See  that  the  wheel 
does  not  wobble  or  flash  badly.  If  it  does,  it 
requires  attention.  Sometimes  a  wheel  may  be 
traced  in  the  dark  by  its  continuous  sparking.  It 
requires  attention  then  surely,  for  if  it  is  not 
attended  to  at  once  it  will  become  so  bad  that  it 
will  have  to  be  thrown  away. 

The  trolley  wheel  is  a  little  thing,  you  may 
think,  and  not  very  expensive  to  replace.  The 
sooner  you  get  over  excusing  yourself  for  inatten- 

229 


230  ELECTRIC    RAILWAY   MOTORS. 

tion  to  little  things  the  sooner  you  will  be  compe- 
tent to  fill  your  position.  Be  very  careful  of  little 
things,  and  there  will  be  no  big  things  to  take  care 
of.  This  seems  like  a  platitude,  but  if  I  can  only 
impress  the  truth  of  this  statement  upon  every 
superintendent  I  will  have  accomplished  a  very 
great  good  to  the  cause  of  street  railroad  practice. 
The  matter  of  proper  tension  of  the  springs  at 
the  base  of  the  trolley  is  one  that  I  am  satisfied  is 
not  usually  given  the  proper  attention.  The  trol- 
ley wheel  is,  I  believe,  in  nine  cases  out  of  ten 
pushed  too  hard  against  the  wire.  It  is  better 
to  err  on  the  other  side,  for  if  the  tension  be  too 
slight  it  will  make  itself  manifest,  but  if  it  be  too 

freat  it  gives   no  evidence  of  the  fact  until  the 
amage  is  clone.     Remember  that  the  resistance  of 
the  contact  betwreen  wheel  and  wire  is  not  materi- 
ally  increased   by  increasing  the  tension    of  the 
spring  within  the  allowable  limits. 

It  is  a  mistaken  idea  that  an  extremely  high  ten- 
sion will  cause  the  trolley  to  keep  the  wire  better 
than  a  moderate  one.  On  the  other  hand,  the  pres- 
sure must  be  sufficient  to  keep  the  wheel  at  its 
enormous  speed  from  "tapping" — that  is,  from 
jumping  momentarily  from  the  wire — which.it  is 
apt  to  do  if  it  happens  to  be  a  little  eccentric  or 
otherwise  runs  a  little  unevenly. 

In  the  earlier  days,  when  we  did  not  know  so 
much  about  these  things  as  we  do  now,  I  remem- 
ber seeing  ai?  electric  road  that  was  operated  by  a 
superintendent  who  believed  there  was  much  to  be 
gained  by  a  stiff  pressure  ;  in  fact,  he  carried  the 
idea  to  an  extreme  even  for  those  days.  The  result 
was  that  his  trolley  lifted  the  wire  a  couple  of  feet 
as  it  passed  along,  and  as  the  car  jolted  and  rocked 
it  set  the  trolley  wire  into  such  violent  vibration 


INCANDESCENT   LAMPS.  231 

that  the  motion  imparted  by  one  car  to  the  wire 
would  often  actually  throw  the  wire  off  the  trolley- 
wheel  of  another  car  some  distance  either  in  the 
rear  or  in  advance.  He  had,  in  fact,  commenced 
running  with  too  tight  a  spring,  and  had  sought  to 
correct  the  difficulty  by  tightening  it  still  more, 
which,  of  course,  only  made  matters  worse.  His 
trolley  wheels  rapidly  wore  out,  and,  worse  than 
this,  his  hangers  were  knocked  to  pieces  in  a  very 
short  time,  and  once  when  I  was  in  the  car,  our 
own  trolley  getting  off,  the  pole  struck  a  span  wire, 
not  only  snapping  the  trolley  pole  off,  but  bring- 
ing down  the  whole  overhead  structure.  This  man, 
finally  learning  his  mistake,  went  to  the  other 
extreme,  perhaps,  but  he  became  a  firm  convert  to 
the  loose  spring. 

INCANDESCENT    LAMPS. 

Remember  that  your  lamps  are  in  series,  and 
that  any  defect  in  one  is  visited  upon  all  the  others. 
If  one  lamp  breaks,  the  circuit  is  broken  ;  or  if 
one  be  not  screwed  in  sufficiently  tight  to  make 
connection,  none  of  them  will  burn.  If,  therefore, 
your  lamps  refuse  to  burn,  examine  them  individ- 
ually to  discover  the  fault  before  condemning  your 
lamp  circuit.  The  situation  of  the  car  lamp  is  an 
exceedingly  trying  one  to  fill.  In  the  first  place 
there  is  the  constant  jar  of  the  car,  which  tends  to 
break  the  filament,  and  in  the  second  there  is  the 
great  variation  in  E.  M.  F.  to  which  it  is  subjected. 
The  line  current  is  apt  to  vary  from  450  volts  to 
520  or  more,  which  is,  we  will  say,  a  variation  of 
fifteen  per  cent. 

Now  experience  has  proved  that  an  increase 
of  three  per  cent,  in  the  voltage  above  that  for 


232  ELECTRIC    RAILWAY    MOTORS. 

which  the  lamp  was  intended  will  divide  its  life 
by  two.  For  instance,  if  a  100-volt  lamp  has  a 
life  of  1000  hours  when  used  on  a  100-volt  cir- 
cuit, it  will  only  have  a  life  of  500  hours  if  the 
pressure  is  increased  to  103  volts. 

The  illumination  given  by  a  lamp  varies  even 
more  widely  with  the  pressure  than  does  its  life. 
No  definite  law  has  as  yet  been  discovered  as  to 
this,  but  we  know  the  temperature  increases  as 
the  square  of  the  current,  and  as  the  current  will 
be  proportional  to  the  pressure,  we  may  say  that 
the  temperature  will  increase  as  the  square  of  the 
pressure  ;  the  illumination  will,  however,  vary 
more  widely  than  this,  its  variation  being  estimated 
by  some  as  being  as  the  fifth  power  of  the  pressure. 
These  statements  being  true,  or  approximately 
true,  one  sees  at  once  the  strain  to  which  a  street 
car  lamp  is  put. 

If  your  lamps  are  already  burning  at  a  very 
high  pressure — that  is,  at  a  pressure  above  that  for 
which  they  were  intended,  or,  in  other  words,  if 
they  are  burning  with  high  efficiency — a  compara- 
tively small  increase  in  pressure  will  break  them 
in  a  short  time.  The  rule  is,  therefore,  in  street 
cars  not  to  use  a  high  efficiency  lamp  ;  first,  because 
under  the  conditions  the  light  it  will  give  will  vary 
too  widely  ;  and  second,  because  its  life  must 
necessarily  be  a  very  short  one.  A  low  efficiency 
lamp  should  always  be  chosen,  for  then,  with  the 
wide  variations  of  pressure  to  which  it  is  subjected, 
the  variation  in  light  will  be  less  apparent  and  its 
life  be  much  longer.  Then,  again,  be  careful  that 
all  the  lamps  on  a  car  are  of  as  nearly  the  same 
resistance  as  possible — exactly  the  same,  if  that 
can  be  arranged,  for  it  is  not  enough  that  the  five 
lamps  shall  in  the  aggregate  absorb  500  volts  ; 


CONCLUSION.  233 

the}r  must  each  absorb  the  same  fraction  of  this — 
10cT  volts.  If  one  lamp  absorbs  110  volts  and 
another  but  90,  the  average  is  maintained,  but  the 
one  that  absorbs  110  volts  will  burn  out  much  the 
quicker.  Lamps  have  often  been  very  unjustly  con- 
demned simply  because,  being  of  high  resistance, 
they  have  burned  out  first  when  put  in  the  same 
series  with  other  lamps,  either  of  the  same  make 
or  of  another,  that  were  of  low  resistance. 

CONCLUSION. 

I  cannot  better  illustrate  the  part  which  a  com- 
petent superintendent  can  play  in  the  general 
efficiency  of  a  road  or  a  system  than  by  recalling 
an  incident  that  occurred  some  years  ago  in  a 
Western  city.  Electric  railroads  were  then  com- 
paratively new.  In  this  city  there  were  two  street 
railroad  companies — one  a  large  corporation  own- 
ing nearly  all  the  lines  in  the  city,  and  the  other 
a  small  corporation  owning  but  one  line,  and  that 
a  short  one  not  more  than  3£  miles  long.  The 
large  corporation  equipped  one  of  its  lines  with 
the  double  trolley  system,  and  the  small  corpora- 
tion equipped  its  line  with  the  single  trolley. 
Both  lines  were  of  about  the  same  length,  but  that 
of  the  small  corporation  abounded  in  long  and 
steep  grades,  one  of  which  reached  13^  per  cent, 
at  one  point;  while  the  other,  although  by  no 
means  level,  was  a  much  easier  line  to  operate. 

A  spirit  of  rivalry  sprang  up  between  the  two 
lines  which  was  heightened  by  a  lawsuit  in  which 
the  single  trolley  road  was  made  the  defendant  (it 
was  one  of  the  telephone  cases),  and  in  which  the 
double  trolley,  though  not  a  party  to  the  suit,  fur- 
nished much  of  the  testimony  for  the  plaintiff. 
The  double  trolley  people  were  called  in  to  prove 


234  ELECTEIC    RAILWAY   MOTORS. 

that  the  double  trolley  was  better  than  the  single 
trolley  ;  and,  among  other  arguments,  showed 
that  with  the  double  trolley  the  car  was  inde- 
pendent of  the  condition  of  the  track,  and  could 
run  under  circumstances  (such  as  heavy  snow) 
where  the  single  trolley  would  be  unable  to  get 
current  through  its  motors.  That  suit  was  decided 
in  favor  of  the  parties  for  whom  the  double  trolley 
people  testified. 

Winter  came  on,  and  with  it  a  heavy  snowfall. 
The  double  trolley  road  had  every  advantage  as  to 
track  and  system  to  meet  this  emergency,  but  the 
single  trolley  road  had  the  more  efficient  superin- 
tendent. There  is  not  a  street  railroad  man  in  the 
country  who  would  not  know  his  name  if  I  men- 
tioned it.  He  kept  the  snow  off  his  tracks  and 
weathered  the  storm  without  stoppage  of  cars. 
The  double  trolley  superintendent,  less  alive  to  the 
situation,  tried  to  run  on  top  of  the  snow,  and  his 
whole  system  was  blocked  for  a  day.  The  fact  of 
the  blockade  of  the  double  trolley  system  and  the 
successful  weathering  of  the  storm  by  the  single 
trolley  system  was  telegraphed  all  over  the 
country  and  taken  by  the  masses  as  evidence  of 
the  superiority  of  the  single  over  the  double  trol- 
ley. For  that  special  emergency,  at  least,  the  facts 
were  exactly  the  reverse.  The  true  significance 
of  the  circumstance  was  that  the  single  trolley 
road  had  the  better  superintendent,  but  the  public 
did  not  understand  it  in  that  way.  So  you  must 
do  much  for  which  you  will  receive  no  credit  from 
the  public  at  large  ;  but  if  you  keep  your  cars 
going  and  keep  them  from  wearing  out,  and  do 
this  at  a  minimum  expense,  your  employers  will 
know  it  and  give  you  full  credit. 


INDEX. 


Advice  to  Readers,  28 

Air  Gap,  59 

Alternating  Current  Dynamo,  85 

Alternating  Currents,  Rectification 

of,  86,  146 

Ammeter,  27,  48,  50,  51,  54 
Ampere,  12,  13,  15,  81 
Amperemeter  (see  Ammeter) 
Ampere-Turn,  58,  90 
Analogy  between    Electricity  and 

Magnetism,  60 

Analogy  between  Water  and  Elec- 
trical Distribution,  116 
Analogy  of  Leaky  Pipe  and  Mag- 
netic Leakage,  65 
Analogy  of   Lines    of    Force  and 

Elastic  Strings,  67 
Analogy  of  the  Dog,  10 
Analogy  of  the  Pipe,  13, 15 
Analogy  of  the  Resistance  of  Rusty 
Pipes  and   Poor  Electrical  Con- 
dnctors,  14,  16,  29 
Analogy  of  the  Rotary  Fan,  136 
Analogy  of  the  Waterfall,  12 
Analogy  of  Waterwheel,  51 
Armature  Coll,  Direction   of  Cur- 
rent in,  85 

Armature  Coils,  Shifting  of,  96 
Armature  Coil,  Reversal  of  Current 

in,  80 

Armature  Coils,  Stripping  of,  97 
Armature,  Eddy  Currents  in,  93 
Armature,  Heating  of,  94 
Armatures,  Closed  Coil,  100,  151 
Armatures,  Drum,  102 
Armatures,  Open  Coil,  100 
Armatures,  Ring,  102 
Armature,  Slotted ,  95 
Arrangement  in  Multiple,  109,  112 
Arrangement  in  Parallel,  109.  112 
Arrangement  in  Series,  109, 112 
Automatic  Block  System,  184 
Automatic  Cut-out,  183 
Axis  of  Commutation,  88, 151 


Battery,  Cost  of  Making,  32 

Battery,  Directions  for  Making,  32 

Battery,  Direction  of  Current  in,  34 

Battery,  Dry,  33 

Battery,  Sal-Ammoniac,  32 

Battery,  Salt  Water,  32 

Battery,  Zinc-Carbon,  30 

Bearings,  226 

Bell,  Magneto,  224 

Binding  Wires,  95 

Block  System,  Automatic,  184 

Braking,  Electrical,  184 

Brass,  Zinc,  Iron.  Rusty  Pipes, 
Resistance  offered  by,  14,  16 

Building  up  of  Dynamo,  130 

Circuit,  Derived  (see  Shunt  Circuit) 

Circuit,  Shunt,  53 

Clearance,  95 

Clinics,  Motor,  218 

Closed  Coil  Armatures,  100, 151 

Closed  Conduit  System,  190 

Commutated  Field  Control,  169 

Commutation,  Axis  of,  88,  151 

Commutation,  Line  of,  151 

Commutation  of  Currents,  86 

Commutator,  88,  89,  221 

Compass,  35,  37 

Compound  Dynamo,  130 

Compromise  Poles  (see  Resultant 
Poles) 

Conductors,  Poor,  15 

Conduit  System,  187 

Conduit  System,  Closed,  190 

Conduit  System,  Love,  188 

Conduit  System,  Siemens  & 
Halske,  188 

Consequent  Poles,  104 

Controllers,  228 

Conversion  of  Electrical  into  Me- 
chanical Units,  27 

Conversion  of  Motor  into  Dynamo, 
184 

Counter  Electromotive  Force,  153 

Counter  Electromotive  Force,  am 


235 


236 


INDEX. 


Essential  Factor  in  the  Power  of 

a  Motor,  155 
Counter  Electromotive  Force  and 

Ohm's  Law,  154 
Counter  Electromotive  Force  and 

Resistance,  154,  157,  160 
Counter  Electromotive  Force  and 

Speed  regulation,  157 
Counter  Electromotive  Force,  for- 
merly a  Bugbear,  155 
Counter  Electromotive  Force,  the 

Measure  of  Work,  155, 162 
Crosby  and  Bell,  161 
Cross  Connection  of  Coils,  124 
Current,  Flow  of,  13 
Currents    and     Magnets,     Mutual 

Effects  of,  38 

Currents,  Commutation  of,  86 
Currents,    Deflection    of     Needle 

by,  38 

Cut-out,  Automatic,  183 
Deflection  of  Needle  by  Currents,  38 
Demagnetization  by  Shock,  47 
Derived  Circuit,  (see  Shunt  Circuit) 
Direction  of  Current  in  Armature 

Coil,  85 
Direction  of  Rotation   of  Electric 

Motor,  141 
Directions  to  Motormen,  Specific, 

201 

Dog,  Analogy  of  the,  10 
Drop,  134 
Drop  Method  of  Locating  Faults, 

Drum  Armatures,  102 

Dynamo,  Alternating  Current,  85 

Dynamo,  Building  up  of,  130 

Dynamo  Compound,  130 

Dynamo,  Continuous  Current,  80 

Dynamo-Electric  Principle,  129 

Dynamo  Over  Compounded,  135 

Dynamo  Series,  130 

Dynamo,  Shunt,  130 

Dynamo,  The  Reversibility  of,  135 

Earth  a  Magnet,  46 

Eddy  Currents  in  Armature,  93 

Effect  of  Change  of  Length    and 

Size  of  Conductor,  19 
Electrical  Braking,  184 
Electrical  Horse  Power,  23, 148 
Electrical  into   Mechanical  Units, 

Conversion  of,  27 
Electrical  Pressure,  21,  90 
Electric  Current  and  its  Properties, 

28 

Electric  Motor,  139 
Electric  Motor,  Direction  of  Rota- 
tion of,  141 


Electro   and    Permanent    Magnets 

Compared,  44 

Electro-Magnet,  43,  44,  54,  55,  56 
Electro-Magnet,  Construction  of,  72 
Electro-Magnet,     Tractive     Power 

of,  74 

Electro-Magnetic  Indnction,'75 
Electromotive  Force,  21,  23  90 
Electromotive  Force  and  Strength 

of  Field,  134 
Energy,  22 

Example,  Test  for  Insulation,  225 
Examples,  Given  C.,  L.,  and  E.  to 

find  R.,  19 
Examples,  Given  C.,  L.,  and  R.  to 

find  E.,  20 
Examples,  Given  C.  and  R.  to  find 

H.  P.,  25 
Examples,  Given  E.  and  R.  to  find 

C.,  18 
Examples,  Given  E.  and  R.  to  find 

H.  P.,  24 
Examples,  Given  H.  P.  and  E.  to 

find  C.,  26 
Examples    in    Speed    Regulation, 

163,166, 
Expenses,  Standard  of  Car  Mile, 

216 

Faults,  Locating,  220, 223 
Feeder  Wire,  184 
Flow  of  Current,  13 
Flux,  Resistance  to,  CO 
Foot  Pound  per  Second,  22,  23 
Force,  Electromotive,  21,  23,  90 
Foucault  Currents,  94 
Friction,  13 

Friction,  Heat  Caused  by,  13 
Fundamental  Units  of  Electricity 

15 

Galvanic  Battery,  Principle  of,  30 
Galvanometer,  40,  78,  223 
Galvanometer,  Convenient  Coil  for, 

41 

Galvanometer,  Directions  for  Mak- 
ing, 40 

Gearing,  Double  Reduction,  149 
Gearing,  Single  Reduction,  150 
Gearless  Motor,  150 
Gears  and  Pinions,  227 
Heat  Causf  d  by  Friction,  13 
Heating  of  Armature,  94 
Horse  Power,  Electrical,  23,  24,  148 
Horse  Power,  Mechanical,  22,  23, 

148 

Induced  Poles,  152 
Inertia,  159 

Inspectors,  Instructions  to,  213 
Instructions  to  Inspectors,  213 


INDEX. 


237 


Instructions  to  Superintendents,  213 

Insulation  Test,  224 

Intra-Mnral  Railroad,  170 

Iron,  Annealed,  Magnetism  of,  43, 

Iron,  Caet,  Magnetism  of,  45 

John  Scott  Legacy  and  Medal,  The, 
184 

Jobnston-Lundell  System,  169 

Kilowatt,  24 

Lamination  of  Core,  93 

Lamps,  High  Efficiency,  232 

Lamps,  Incandescent,  231 

Lamp",  Low  Efficiency.  232 

Law  of  Flow  in  Multiple  Circuits, 
132 

Law  of  Heating  Effects  of  Current, 
159 

Law  of  Magnetic  Flux,  56 

Law  of  Magnetizing  Effect  of  Sole- 
noid, 57 

Leakage,  Magnetic,  64,  65 

Leonard  System,  176,  177 

Like  and  Unlike  Poles,  Mutual  Ef- 
fect of,  38 

Line  of  Commutation  (see  Axis  of 
Commutation), 

Lines  of  Force,  59,  60,  61, 62,  140 

Locating  Faults,  220,  223 

Lowell  &  Suburban  St.  Ry.  Co.,  216 

Magnetic  Circuit  Closed,  63,  75 

Magnetic  Curves,  67 

Magnetic  Leakage,  64,  65 

Magnetic  Poles,  Definition  of,  63 

Magnetic  Pressure,  57 

Magnetic  Saturation,  62 

Magnetism  and  Current,  «2 

Magnetism,  Change  of  Direction 
of,  44 

Magnetism,  Conductors  of ,  59,  64 

Magnetism,  Electro,  43,  44.  54 

Magnetism  of  Soft  Annealed  Iron, 
43,44,54 

Magnetism  of  Tempered  Steel,  43, 
44,54 

Magnetism,  Permanent,  43,  44,  54 

Magnetism,  Residual,  74 

Magnets,  Multipolar,  104,  121,  125, 
127 

Magneto-Electric  Machine.  127 

Magneto  Bell,  224 

Magnetization  Assisted  by  Shock, 
46 

Magnetization  by  Contact,  45 

Magnetization  by  Proximity,  45 

Magnetization  by  the  Earth,  46 

Magnetization  of  Soft  Iron  Nearly 
Instantaneous.  44,  75 


Magnetization  of  Tempered  Steel, 

Time  Required  for,  44 
Magneto-Motive  Force,  57,  58 
Magnet,  Position  of,  when  free  to 

Move  in  Horizontal  Plane,  37 
Magnet  without  Poles,  64 
Management    of    Street    Railway 

Motors,  191 

Measuring  Instruments,  48 
Mechanical   Horse  Power,  22,  23, 

148 

Motor  Clinics,  218 
Motor,  Electric,  139 
Motor,   Electric,  Consumes  Volts, 

51,  119 
Motor,  Electric,  does  not  Consume 

Current,  51,  119 
Motor  Fails  to  Start,  199 
Motor,  Gearless,  150 
Motor,  Slow  Speed,  150 
Motor  Stops,  199 

Multiple  Arc  Arrangement,  109,  112 
Multiple  Circuits,- Law  of  Flow  in, 

132 


125, 


Multiplying  Effect  of  Coils,  40 
Mnltipolar  Magnets,  104,  121, 


127 


Mutual   Effects    of  Currents   and 

Magnet*,  38 
Mutual  Effect  of  Like  and  Unlike 

Poles,  38 

North-seeking  Pole,  46 
North-seeking    Pole    in  Reality    a 

South  Pole,  46 
Ohm,  14,  15,  18,  21 
Ohm,  George  Simon,  16 
Ohm's  Law,  16,  17,  21 
Ohmmeter,  53 
Open  Coil  Armatures,  100 
Overwork,  What  Constitutes,  99 
Permanent  and   Electro    Magnets 

Compared,  44 

Permanent  Magnet,  43,  44,  54,  55 
Perry  System.  181 
Pinions  and  Gears,  227 
Pipe,  Analogy  of,  13,  15 
Polarity   Dependent  on  Direction 

of  flow  of  Current   in  Solenoid, 

55 
Polarity,  Effect  on,  of  Direction  of 

Flow  of  Current, 
Polarity  Independent  of  Direction 

of  Solenoid,  55 
Polarity,  Reversing  by  Reversing 

Connections,  72 

Polarity,  Rule  for  Determining,  71 
Poor  Conductors,  15 
Potential,  Difference  of,  52.  53 


238 


INDEX. 


Pressure,  Electrical,  21,  90 
Pressure,  Magnetic,  57 
Principle  of  Galvanic  Battery,  30 
Production  of  Steady  Currents,  88 
Rate  of  Flow,  21  (see  Ampere) 
Rate  of  Work,  22 
Readers,  Advice  to,  28 
Rectification    of  Alternating    Cur- 
rents. 86,  146 

Remarks  of  P.  P.  Sullivan,  216 
Residual  Magnetism,  74 
Resistance,  14,  21,  48,  53,  54,  56 
Resistance,  Measurement  of,  53 
Resistance  offered  by  Iron,  Brass, 

Zinc,  Rusty  Pipes,  14, 16 
Resistance  to  Magnetic  Flux,  56 
Resultant  Poles,  151 
Reversal    of  Current  in  Armature 

Coil,  80 

Reversibility  of  the  Dynamo,  135 
Rheostat,  161 
Rheostat  Control,  169 
Rheostat  Regulation,  161 
Ring  Armatures,  102 
Saturation,  Magnetic,  62 
Separately  Excited  Machine,  128 
Series  Arrangement,  109,  112 
Series  Dynamo,  130 
Series  Parallel  Control,  169 
Series  System,  181 
Shifting  of  Armature  Coils,  96 
Shunt  Circuit,  53 
Shunt  Dynamo,  130 
Slotted  Armature,  95 
Solenoid,  Directions  for  Making,  34 
Solenoid,  Magnetism  and  Property 

of,  42 
Solenoid,  Magnetism  Due  Solely  to 

Current,  43 
Solenoid,  Magnetization  by,  35,  48, 

55,57 

Solenoid  of  one  Turn,  49 
Solenoid  of  two  Turns,  49 
Solenoid  of  three  Turns.  50 
Solenoid  of  any  Number  of  Turns, 

50 


Solenoid,    Polarity   Produced    by, 

36,55 

Solenoid,  Properties  of,  42,  47,  57 
Sparking  at  the  Commutator,  194 
Specific  Directions  to  Motormen, 

201 
Speed  Control,  Johnston- Lundell, 

173 

Speed  Control,  Perry  System,  185 
Speed  Regulation,  Requirements  of, 

161 

Standard  of  Car  Mile  Expenses,  216 
Steady   Currents,    Production     of, 

88 
Storage  Battery,  Disadvantages  of, 

186 

Storage  Battery,  Inherent,  185 
Storage  Battery  Traction,  185 
Strength    of    Field   and    Electro- 
motive Force,  134 
Stripping  of  Armature  Coils,  97 
Sullivan,  P.  P.,  Remarks  of,  216 
Superintendents,    Instructions    to, 

213 

Surface  Contact  System,  174 
Technical  Terms,  9, 15 
Tempered  Steel,  Magnetism  of,  43, 

Test  for  Insulation,  224 

Torque,  144 

Translating,  Current  Characteristics 

in,  116 

Translating  Device,  110 
Trolley  Wheels,  229 
Units  of  Electricity,  Fundamental, 

15 

Volt,  12,  13,  15,  23 
Voltage,  21 

Voltmeter,  27,  48,  51,  53,  54 
Voltmeter,  Function  of,  53 
Waterfall,  Analogy  of  the,  12 
Watt,  23,  24 

What  Constitutes  Overwork,  99 
Whoatstone  Bridge,  53 
Work,  148 
Work,  Rate  of,  22,  24,  148 


.^^J&^S  £•    L 1  crn^/J  ^^*v 
j        ^  OF  THE  \ 

ftfNIVERSITT) 

^^CALJFORN^:.^^ 


Elementary 
Electro -Technical  Series. 

EDWIN  J.  HOUSTON,  Ph.D.  and  A.  E.  KENNELLY,  D.Sc. 


Alternating  Electric  Currents,  Electric  Incandescent  Light- 
Electric  Heating,  ing, 

Electromagnetism,  Electric  Motors, 

Electricity  in  Electro-Thera-  Electric  Street  Railways, 

peutics,  Electric  Telephony, 

Electric  Arc  Lighting,  Electric  Telegraphy. 


Cloth,  profusely  illustrated.  Price,  $1.OO  per  volume. 


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RECKNT  PROORESS 


ELECTRIC  RAILWAYS. 

Being  a  Summary  of  Current  Progress  In  Electric  Railway 

Construction,  Operation,  Systems,  Machinery, 

Appliances,  etc. 

By  CARL  HERINQ, 

AUTHOR  OF 

"  Principles  of  Dynamo-Electric  Machinery ',"  etc.,  etc,^  etc. 

Cloth,     389  pages,  104  illustrations,     Price,  $1,00, 

The  details  connected  with  electric  street  railways  have  become 
so  numerous  and  the  systems  so  varied  that  the  reader  is  at  a  loss 
when  he  wishes  specific  information  in  regard  to  many  desirable 
points,  which  can  scarcely  be  expected,  as  a  rule,  in  a  general 
treatise  on  the  subject.  Bering's  "  Recent  Progress  in  Electric 
Railways "  is  particularly  valuable  from  its  treatment  of  details, 
and  elaborates  a  number  of  features  that  have  heretofore  received 
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roads  and  underground  tunnel  conduit  systems, — while  the  section 
on  construction  and  operation  is  very  full,  and  gives  much  recent 
engineering  and  financial  data.  The  historical  notes  and  statistics 
on  the  development  of  the  industry  will  be  found  complete  and 
reliable.  The  hundred  or  more  pages  devoted  to  the  consideration 
of  details  and  recent  improvements  contain  information  of  the 
greatest  value  that  otherwise  could  only  be  obtained  by  a  laborious 
search  through  periodical  literature.  Here  the  latest  inventions 
and  developments  in  street-railway  motors,  apparatus,  and  fittings 
are  described  and  illustrated  in  great  detail,  thus  supplying  the 
omissions  from  more  general  treatises. 

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REFERENCE   BOOK  OF 

Tables  and  Formulas 

FOR 

ELECTRIC  STREET  RAILWAY  ENGINEERS. 

ABRANGED   AND   COMPILED 

By   E.   A.   MERRILL, 

Author  of  "  Electric  Lighting  Specifications  for  the  Use  of 
Engineers  and  Architects. ' ' 

Flexible  Morocco.    Price,  $1.OO. 

To  a  busy  man  the  value  of  a  reference  book  depends  largely  on  the 
facility  with  which  he  can  get  from  it  the  information  he  desires.  In  the 
larger  works  the  labor  involved  in  seeking  out  information,  which  perhaps 
is  scattered  through  several  sections  and  encumbered  with  examples  and 
explanations  already  tamiliar  to  the  engineer,  is  often  exceedingly  annoy- 
ing, especially  when  many  times  repeated.  It  is  the  object  ot  this  refer- 
ence book  to  avoid  such  annoyances  and  meet  a  practical  need  by  collect- 
ing and  arranging  in  a  concise,  logical  order  those  tables  and  formulas 
which  are  in  constant  use  by  the  electrical  street-railway  engineer  in 
making  estimates,  ordering  material,  on  construction  work,  etc.  All 
superfluous  examples  and  explanations  have  been  excluded,  as  well  as 
unnecessary  extensions  of  formulre  into  tables  when  such  extensioi:s 
consist  only  in  the  simplest  mathematical  processes.  Not  only  has  con- 
siderable care  been  taken  in  selecting  and  checking  material  compiled 
directly,  but  several  original  tables  and  formulae  have  been  added, 
especially  in  the  sections  on  track  and  overhead- work,  which  will  save 
many  calculations.  Furthermore,  many  tables  and  formulae  have  been 
extended  and  modified  to  meet  the  conditions  imposed  in  street-railway 
work.  The  practical  arrangement  of  the  work,  its  condensed  style  and 
convenient  form,  will  recommend  it  to  every  street-railway  engineer. 
Every  heading  is  in  bold-faced  type,  which  easily  catches  the  eye  as  one 
glances  over  the  page,  thus  materially  aiding  quick  reference,  and  as  a 
further  aid  a  complete  cross-index  is  added.  The  book  is  bound  in 
flexible  covers  and  is  of  convenient  size  to  carry  in  the  pocket. 

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POSTAGE  PREPAID,  to  any  address  in  theivorld,  on  receipt  of  price. 


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Recent    Progress    in   Electric    Railways. 

Being  a  Summary  oi  -Current  Advance  in  Electric  Rail- 
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